/* ============================================
   ⚡ Giải tích mạch made by Phuthieunang
   Vibrant • Animated • Modern
   ============================================ */

* { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --c-pink: #ec4899;
  --c-pink-light: #f9a8d4;
  --c-pink-deep: #be185d;
  --c-rose: #fb7185;
  --c-purple: #a855f7;
  --c-cyan: #06b6d4;
  --c-blue: #3b82f6;
  --c-yellow: #fbbf24;
  --c-orange: #fb923c;
  --c-green: #10b981;
  --c-red: #ef4444;
  --c-bk: #0d4eb8;
  --c-bk-light: #1f7ce8;

  --bg: #fef5f9;
  --bg-soft: #fef0f5;
  --bg-card: rgba(255, 255, 255, 0.92);
  --bg-card-solid: #ffffff;
  --text: #1f1147;
  --text-muted: #7c5b75;
  --border: rgba(236, 72, 153, 0.18);

  --grad-hero: linear-gradient(135deg, #ec4899 0%, #f97316 35%, #fbbf24 60%, #ec4899 100%);
  --grad-card: linear-gradient(135deg, #fff5f9 0%, #ffe0ef 100%);
  --grad-button: linear-gradient(135deg, #ec4899 0%, #be185d 100%);
  --grad-button-pink: linear-gradient(135deg, #ec4899, #fb7185);
  --grad-button-yellow: linear-gradient(135deg, #fbbf24, #ec4899);
  --grad-button-green: linear-gradient(135deg, #10b981, #06b6d4);
  --grad-rose: linear-gradient(135deg, #ec4899 0%, #fbbf24 100%);

  --shadow-sm: 0 2px 8px rgba(236, 72, 153, 0.10);
  --shadow-md: 0 8px 24px rgba(236, 72, 153, 0.18);
  --shadow-lg: 0 16px 48px rgba(236, 72, 153, 0.28);
  --shadow-glow: 0 0 50px rgba(236, 72, 153, 0.55);
  --shadow-rose: 0 0 30px rgba(236, 72, 153, 0.4), 0 0 60px rgba(251, 191, 36, 0.3);

  --radius: 16px;
  --radius-sm: 10px;
}

html { scroll-behavior: smooth; }

body {
  font-family: 'Be Vietnam Pro', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  font-size: 16px;
  line-height: 1.6;
  color: var(--text);
  background: var(--bg);
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  overflow-x: hidden;
}

body.splash-active {
  overflow: hidden;
  height: 100vh;
}

/* ============================================
   💥 SPLASH / CIRCUIT INTRO
   ============================================ */
.splash {
  position: fixed;
  inset: 0;
  z-index: 9999;
  display: grid;
  place-items: center;
  background:
    radial-gradient(circle at 25% 25%, rgba(255, 110, 199, 0.35) 0%, transparent 45%),
    radial-gradient(circle at 75% 75%, rgba(6, 182, 212, 0.4) 0%, transparent 45%),
    radial-gradient(circle at 50% 50%, rgba(168, 85, 247, 0.3) 0%, transparent 60%),
    linear-gradient(135deg, #1a0b3d 0%, #0a0420 50%, #150829 100%);
  background-size: 200% 200%;
  animation: splashBg 6s ease-in-out infinite;
  overflow: hidden;
  transition: opacity 0.8s ease, transform 0.8s ease;
}

.splash-circuit {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
  opacity: 0.85;
}

.splash-circuit .trace {
  stroke-dasharray: 2000;
  stroke-dashoffset: 2000;
  animation: drawTrace 2.5s ease-out forwards;
}

.splash-circuit .t1 { animation-delay: 0.1s; }
.splash-circuit .t2 { animation-delay: 0.4s; }
.splash-circuit .t3 { animation-delay: 0.6s; }
.splash-circuit .t4 { animation-delay: 0.9s; }
.splash-circuit .t5 { animation-delay: 1.1s; }

@keyframes drawTrace {
  to { stroke-dashoffset: 0; }
}

.splash-circuit .comp {
  opacity: 0;
  animation: compFadeIn 0.6s ease forwards;
}

@keyframes compFadeIn {
  from { opacity: 0; transform: scale(0.5); }
  to { opacity: 1; transform: scale(1); }
}

.splash-circuit .splash-sine {
  stroke-dasharray: 4 8;
  animation: sineFlow 1.5s linear infinite;
}

@keyframes sineFlow {
  to { stroke-dashoffset: -24; }
}

.splash-circuit .splash-dots circle {
  animation: dotPulse 3s ease-in-out infinite;
}

@keyframes dotPulse {
  0%, 100% { opacity: 0.3; r: 2; }
  50% { opacity: 1; r: 3.5; }
}

.splash-circuit .electron {
  filter: drop-shadow(0 0 8px currentColor);
}

@keyframes splashBg {
  0%, 100% { background-position: 0% 0%; }
  50% { background-position: 100% 100%; }
}

.splash.is-leaving {
  opacity: 0;
  transform: scale(1.1);
  pointer-events: none;
}

.splash::before, .splash::after {
  content: '';
  position: absolute;
  border-radius: 50%;
  filter: blur(60px);
  opacity: 0.7;
  animation: splashOrb 6s ease-in-out infinite;
}

.splash::before {
  width: 400px;
  height: 400px;
  background: #ff6ec7;
  top: -100px;
  left: -100px;
}

.splash::after {
  width: 500px;
  height: 500px;
  background: #06b6d4;
  bottom: -150px;
  right: -150px;
  animation-delay: -3s;
}

@keyframes splashOrb {
  0%, 100% { transform: translate(0, 0) scale(1); }
  33% { transform: translate(60px, -40px) scale(1.15); }
  66% { transform: translate(-40px, 60px) scale(0.9); }
}

.splash-content {
  position: relative;
  z-index: 5;
  text-align: center;
  padding: 24px;
  max-width: 760px;
}

.splash-equation {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  gap: 6px;
  font-family: 'Times New Roman', serif;
  font-style: italic;
  font-size: clamp(0.95rem, 2vw, 1.3rem);
  color: rgba(255, 255, 255, 0.7);
  background: rgba(255, 255, 255, 0.06);
  backdrop-filter: blur(10px);
  border: 1px solid rgba(255, 255, 255, 0.12);
  padding: 10px 22px;
  border-radius: 999px;
  margin-bottom: 24px;
  animation: splashFadeIn 1s ease 1.6s both, eqGlow 3s ease-in-out 2.6s infinite;
}

.splash-equation .eq-eq { color: #fbbf24; font-weight: 700; }
.splash-equation .eq-sep { color: rgba(255, 255, 255, 0.3); margin: 0 6px; }
.splash-equation .eq-frac { color: #ff6ec7; font-size: 0.85em; }
.splash-equation sup, .splash-equation sub { color: #06b6d4; font-size: 0.7em; }

@keyframes eqGlow {
  0%, 100% { box-shadow: 0 0 10px rgba(168, 85, 247, 0.3); }
  50% { box-shadow: 0 0 25px rgba(255, 110, 199, 0.5); }
}

.splash-logo-wrap {
  position: relative;
  display: inline-block;
  margin-bottom: 12px;
}

.splash-logo-pulse {
  position: absolute;
  inset: 0;
  border: 2px solid #fbbf24;
  border-radius: 50%;
  opacity: 0;
  animation: logoPulse 2s ease-out 1.5s infinite;
  pointer-events: none;
}

@keyframes logoPulse {
  0% { opacity: 0.8; transform: scale(0.7); }
  100% { opacity: 0; transform: scale(2.2); }
}

.splash-logo {
  font-size: clamp(5rem, 16vw, 10rem);
  display: inline-block;
  filter: drop-shadow(0 0 60px #fbbf24) drop-shadow(0 0 20px #ff6ec7);
  animation: splashLogo 1.4s cubic-bezier(0.34, 1.56, 0.64, 1) both, splashLogoSpin 3s ease-in-out 1.4s infinite;
  position: relative;
  z-index: 2;
}

@keyframes splashLogo {
  0% { opacity: 0; transform: scale(0) rotate(-180deg); }
  60% { opacity: 1; transform: scale(1.3) rotate(20deg); }
  100% { opacity: 1; transform: scale(1) rotate(0deg); }
}

@keyframes splashLogoSpin {
  0%, 100% { transform: rotate(0deg) scale(1); filter: drop-shadow(0 0 60px #fbbf24) drop-shadow(0 0 20px #ff6ec7); }
  50% { transform: rotate(15deg) scale(1.08); filter: drop-shadow(0 0 80px #ff6ec7) drop-shadow(0 0 30px #06b6d4); }
}

.splash-title {
  font-size: clamp(2.2rem, 7vw, 4.5rem);
  font-weight: 900;
  line-height: 1.05;
  letter-spacing: -0.02em;
  background: linear-gradient(135deg, #fff 0%, #ffe4f1 30%, #fbbf24 60%, #ff6ec7 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: 16px;
  animation: splashTitle 1.2s cubic-bezier(0.4, 0, 0.2, 1) 0.3s both;
  filter: drop-shadow(0 4px 30px rgba(255, 110, 199, 0.5));
}

@keyframes splashTitle {
  0% { opacity: 0; transform: translateY(30px); letter-spacing: 0.4em; filter: blur(20px); }
  100% { opacity: 1; transform: translateY(0); letter-spacing: -0.02em; filter: blur(0); }
}

.splash-author {
  display: inline-block;
  background: linear-gradient(135deg, #fbbf24, #ff6ec7);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  font-weight: 800;
}

.splash-subtitle {
  font-size: clamp(0.95rem, 2.2vw, 1.25rem);
  color: rgba(255, 255, 255, 0.85);
  margin-bottom: 22px;
  font-weight: 500;
  animation: splashFadeIn 1s ease 0.8s both;
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 8px;
  align-items: center;
}

.splash-subtitle .dot-sep { color: rgba(255, 255, 255, 0.4); }

.splash-chips {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 8px;
  margin-bottom: 26px;
  animation: splashFadeIn 1s ease 1.0s both;
}

.splash-chips .chip {
  padding: 6px 14px;
  background: rgba(255, 255, 255, 0.08);
  backdrop-filter: blur(10px);
  border: 1px solid rgba(255, 255, 255, 0.18);
  border-radius: 999px;
  color: white;
  font-weight: 600;
  font-size: 0.82rem;
  letter-spacing: 0.05em;
  transition: all 0.3s;
}

.splash-chips .chip:nth-child(1) { color: #06b6d4; border-color: rgba(6, 182, 212, 0.5); }
.splash-chips .chip:nth-child(2) { color: #ff6ec7; border-color: rgba(255, 110, 199, 0.5); }
.splash-chips .chip:nth-child(3) { color: #fbbf24; border-color: rgba(251, 191, 36, 0.5); }
.splash-chips .chip:nth-child(4) { color: #a855f7; border-color: rgba(168, 85, 247, 0.5); }
.splash-chips .chip:nth-child(5) { color: #10b981; border-color: rgba(16, 185, 129, 0.5); }
.splash-chips .chip:nth-child(6) { color: #fb923c; border-color: rgba(251, 146, 60, 0.5); }

.cta-icon {
  display: inline-block;
  animation: zap 1.5s ease-in-out infinite;
  filter: drop-shadow(0 0 6px #fbbf24);
}

.splash-tagline {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 10px 22px;
  background: rgba(255, 255, 255, 0.1);
  backdrop-filter: blur(20px);
  border: 1.5px solid rgba(255, 255, 255, 0.25);
  border-radius: 999px;
  color: white;
  font-weight: 600;
  font-size: 0.95rem;
  margin-bottom: 36px;
  animation: splashFadeIn 1s ease 1.1s both;
}

.splash-tagline-dot {
  width: 8px;
  height: 8px;
  background: #10b981;
  border-radius: 50%;
  animation: blink 1.5s ease-in-out infinite;
}

@keyframes blink {
  0%, 100% { opacity: 1; box-shadow: 0 0 8px #10b981; }
  50% { opacity: 0.3; box-shadow: 0 0 16px #10b981; }
}

.splash-cta {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 16px 40px;
  background: linear-gradient(135deg, #fff 0%, #ffe4f1 100%);
  color: #1f1147;
  border: none;
  border-radius: 14px;
  font-weight: 800;
  font-size: 1.1rem;
  cursor: pointer;
  box-shadow: 0 0 60px rgba(255, 255, 255, 0.5), 0 0 30px rgba(255, 110, 199, 0.6);
  transition: all 0.3s;
  animation: splashFadeIn 1s ease 1.4s both, splashPulse 2.5s ease-in-out 2.4s infinite;
  position: relative;
  overflow: hidden;
}

.splash-cta::before {
  content: '';
  position: absolute;
  top: 0;
  left: -100%;
  width: 100%;
  height: 100%;
  background: linear-gradient(90deg, transparent, rgba(255, 110, 199, 0.4), transparent);
  animation: shine 3s ease-in-out 2.5s infinite;
}

@keyframes shine {
  0% { left: -100%; }
  100% { left: 200%; }
}

.splash-cta:hover {
  transform: translateY(-4px) scale(1.05);
  box-shadow: 0 0 80px rgba(255, 255, 255, 0.7), 0 0 40px rgba(255, 110, 199, 0.8);
}

@keyframes splashPulse {
  0%, 100% { box-shadow: 0 0 60px rgba(255, 255, 255, 0.5), 0 0 30px rgba(255, 110, 199, 0.6); }
  50% { box-shadow: 0 0 80px rgba(255, 255, 255, 0.7), 0 0 50px rgba(168, 85, 247, 0.7); }
}

@keyframes splashFadeIn {
  0% { opacity: 0; transform: translateY(20px); }
  100% { opacity: 1; transform: translateY(0); }
}

.splash-sparkle {
  position: absolute;
  font-size: 1.5rem;
  pointer-events: none;
  animation: sparkleFloat 4s ease-in-out infinite;
  filter: drop-shadow(0 0 10px currentColor);
}

@keyframes sparkleFloat {
  0%, 100% { transform: translateY(0) rotate(0deg); opacity: 0.7; }
  50% { transform: translateY(-30px) rotate(180deg); opacity: 1; }
}

.splash-skip {
  position: absolute;
  bottom: 24px;
  right: 24px;
  background: rgba(255, 255, 255, 0.1);
  backdrop-filter: blur(12px);
  color: rgba(255, 255, 255, 0.8);
  border: 1px solid rgba(255, 255, 255, 0.2);
  padding: 8px 16px;
  border-radius: 8px;
  font-size: 0.85rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s;
  animation: splashFadeIn 1s ease 2s both;
  z-index: 3;
}

.splash-skip:hover {
  background: rgba(255, 255, 255, 0.2);
  color: white;
}

.splash-rose {
  position: absolute;
  bottom: -40px;
  right: 20px;
  pointer-events: none;
  animation: splashFadeIn 1.2s ease 2.2s both;
}

.splash-rose .rose-petal {
  display: inline-block;
  font-size: 2rem;
  color: #ff6ec7;
  filter: drop-shadow(0 0 12px rgba(251, 191, 36, 0.8));
  animation: roseGlow 4s ease-in-out infinite;
}

.splash-rose .rose-glow {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 120px;
  height: 120px;
  background: radial-gradient(circle, rgba(251, 191, 36, 0.4), transparent 70%);
  transform: translate(-50%, -50%);
  border-radius: 50%;
  animation: rosePulse 3s ease-in-out infinite;
}

@keyframes rosePulse {
  0%, 100% { opacity: 0.5; transform: translate(-50%, -50%) scale(0.8); }
  50% { opacity: 1; transform: translate(-50%, -50%) scale(1.3); }
}

/* ============================================
   🌹 EASTER EGG: type "anhhong" anywhere
   ============================================ */
.rose-celebration {
  position: fixed;
  inset: 0;
  z-index: 9998;
  pointer-events: none;
  display: grid;
  place-items: center;
}

.rose-celebration.is-active {
  animation: roseCelebrationFade 4.5s ease forwards;
}

@keyframes roseCelebrationFade {
  0% { opacity: 0; }
  10% { opacity: 1; }
  85% { opacity: 1; }
  100% { opacity: 0; }
}

.rose-celebration .big-rose {
  font-size: clamp(8rem, 20vw, 14rem);
  filter: drop-shadow(0 0 60px rgba(251, 191, 36, 1)) drop-shadow(0 0 30px rgba(255, 110, 199, 1));
  animation: bigRoseAppear 1.2s cubic-bezier(0.34, 1.56, 0.64, 1), roseSpin 3s linear 1.2s;
  color: #ff6ec7;
}

@keyframes bigRoseAppear {
  0% { transform: scale(0) rotate(-360deg); opacity: 0; }
  60% { transform: scale(1.4) rotate(20deg); opacity: 1; }
  100% { transform: scale(1) rotate(0deg); opacity: 1; }
}

@keyframes roseSpin {
  0% { transform: scale(1) rotate(0deg); }
  100% { transform: scale(1.05) rotate(360deg); }
}

.rose-celebration .ah-text {
  position: absolute;
  bottom: 25%;
  left: 50%;
  transform: translateX(-50%);
  font-size: clamp(1.2rem, 3vw, 2rem);
  font-weight: 700;
  color: white;
  text-shadow: 0 0 20px #ff6ec7, 0 0 40px #fbbf24;
  font-style: italic;
  white-space: nowrap;
  opacity: 0;
  animation: ahReveal 1s ease 1.8s forwards;
}

@keyframes ahReveal {
  to { opacity: 1; }
}

/* ============================================
   ✨ ANIMATED BACKGROUND
   ============================================ */
.bg-mesh {
  position: fixed;
  inset: 0;
  z-index: -2;
  background:
    radial-gradient(circle at 15% 20%, rgba(236, 72, 153, 0.25) 0%, transparent 50%),
    radial-gradient(circle at 85% 25%, rgba(251, 191, 36, 0.2) 0%, transparent 50%),
    radial-gradient(circle at 50% 80%, rgba(251, 113, 133, 0.18) 0%, transparent 55%),
    radial-gradient(circle at 90% 90%, rgba(249, 168, 212, 0.25) 0%, transparent 50%),
    var(--bg);
  animation: meshShift 20s ease-in-out infinite;
}

@keyframes meshShift {
  0%, 100% { filter: hue-rotate(0deg); }
  50% { filter: hue-rotate(20deg); }
}

#particles {
  position: fixed;
  inset: 0;
  z-index: -1;
  pointer-events: none;
}

#petals {
  position: fixed;
  inset: 0;
  z-index: 0;
  pointer-events: none;
}

/* ============================================
   ☀️ SUN RAYS (subtle warm accent)
   ============================================ */
.sun-rays {
  position: fixed;
  top: -200px;
  left: -200px;
  width: 600px;
  height: 600px;
  z-index: -1;
  pointer-events: none;
  opacity: 0.5;
  animation: rayRotate 80s linear infinite;
}

.ray {
  position: absolute;
  top: 0;
  left: 50%;
  width: 2px;
  height: 50%;
  transform-origin: bottom;
  background: linear-gradient(to top, transparent, rgba(251, 191, 36, 0.4), rgba(255, 110, 199, 0.3));
  filter: blur(2px);
  animation: rayPulse 4s ease-in-out infinite;
}

.ray.r1 { transform: translateX(-50%) rotate(15deg); }
.ray.r2 { transform: translateX(-50%) rotate(35deg); animation-delay: -1s; }
.ray.r3 { transform: translateX(-50%) rotate(55deg); animation-delay: -2s; }
.ray.r4 { transform: translateX(-50%) rotate(75deg); animation-delay: -3s; }

@keyframes rayRotate {
  to { transform: rotate(360deg); }
}

@keyframes rayPulse {
  0%, 100% { opacity: 0.3; }
  50% { opacity: 0.7; }
}

/* ============================================
   🎉 HERO SECTION (Trang chủ - opening wow)
   ============================================ */
.hero {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 60px 24px 100px;
  text-align: center;
  position: relative;
  overflow: hidden;
}

@media (min-width: 1200px) {
  .hero { padding: 80px 56px 120px; }
}

.hero-bk-pillar {
  display: flex;
  align-items: center;
  gap: 18px;
  margin-bottom: 28px;
  background: rgba(255, 255, 255, 0.7);
  backdrop-filter: blur(14px);
  border: 1.5px solid var(--border);
  border-radius: 18px;
  padding: 14px 24px;
  box-shadow: var(--shadow-sm);
  animation: floatY 4s ease-in-out infinite;
}

.hero-bk-logo {
  width: 64px;
  height: 64px;
  filter: drop-shadow(0 4px 12px rgba(13, 78, 184, 0.3));
}

.hero-bk-text {
  text-align: left;
}

.hero-bk-line {
  font-weight: 800;
  font-size: 0.95rem;
  color: var(--c-bk);
  letter-spacing: 0.04em;
  line-height: 1.2;
}

.hero-bk-sub {
  font-size: 0.78rem;
  color: var(--text-muted);
  margin-top: 2px;
  font-weight: 600;
}

.hero-h1-author {
  background: var(--grad-rose);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  filter: drop-shadow(0 4px 12px rgba(236, 72, 153, 0.4));
}

/* ============================================
   ✨ SIGNATURE NAME — "Phúthieunang"
   Hiệu ứng đặc sắc, hài hòa với nền hồng-vàng
   ============================================ */
.signature-name {
  display: inline-block;
  position: relative;
  font-family: 'Dancing Script', 'Pacifico', 'Brush Script MT', cursive;
  font-weight: 700;
  background: linear-gradient(
    100deg,
    #be185d 0%,
    #ec4899 20%,
    #f97316 38%,
    #fbbf24 52%,
    #ec4899 72%,
    #be185d 100%
  );
  background-size: 220% 100%;
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  filter: drop-shadow(0 0 14px rgba(251, 191, 36, 0.55))
          drop-shadow(0 2px 8px rgba(236, 72, 153, 0.5));
  animation: signatureFlow 5s ease-in-out infinite;
  padding: 0 6px;
  letter-spacing: 0.5px;
  font-size: 1.18em;
  line-height: 1;
  vertical-align: -0.02em;
}

.signature-name::before {
  content: '🌹';
  position: absolute;
  left: -18px;
  top: 50%;
  transform: translateY(-50%) scale(0.6);
  font-size: 0.85em;
  filter: drop-shadow(0 0 6px rgba(251, 191, 36, 0.8));
  animation: signRoseSpin 4s ease-in-out infinite;
  -webkit-text-fill-color: initial;
}

.signature-name::after {
  content: '✦';
  position: absolute;
  right: -14px;
  top: 0;
  font-size: 0.55em;
  color: #fbbf24;
  -webkit-text-fill-color: #fbbf24;
  filter: drop-shadow(0 0 8px #fbbf24);
  animation: signSparkle 2.4s ease-in-out infinite;
}

@keyframes signatureFlow {
  0%, 100% { background-position: 0% 50%; }
  50%      { background-position: 100% 50%; }
}

@keyframes signRoseSpin {
  0%, 100% { transform: translateY(-50%) scale(0.6) rotate(-10deg); }
  50%      { transform: translateY(-50%) scale(0.85) rotate(10deg); }
}

@keyframes signSparkle {
  0%, 100% { opacity: 0.5; transform: scale(0.8) rotate(0deg); }
  50%      { opacity: 1; transform: scale(1.3) rotate(180deg); }
}

/* Bigger version inside hero h1 (chữ rất to) */
.hero h1 .signature-name {
  font-size: 1.05em;
  -webkit-text-fill-color: transparent;
}

.hero h1 .signature-name::after {
  font-size: 0.4em;
  right: -22px;
}

.hero h1 .signature-name::before {
  left: -32px;
  font-size: 0.55em;
}

/* Hero subtitle signature line */
.signature-line {
  display: inline-block;
  background: rgba(255, 255, 255, 0.55);
  backdrop-filter: blur(10px);
  border: 1.5px solid rgba(236, 72, 153, 0.25);
  padding: 6px 18px 6px 24px;
  border-radius: 999px;
  font-weight: 700;
  font-size: 1.05em;
  margin-top: 6px;
  color: var(--c-pink-deep);
  box-shadow: 0 4px 18px rgba(236, 72, 153, 0.2);
}

.signature-spark {
  display: inline-block;
  color: #fbbf24;
  margin-left: 4px;
  filter: drop-shadow(0 0 8px #fbbf24);
  animation: signSparkle 2s ease-in-out infinite;
}

/* Decorative roses around hero */
.hero-rose {
  position: absolute;
  font-size: clamp(2rem, 5vw, 3.5rem);
  pointer-events: none;
  filter: drop-shadow(0 0 18px rgba(251, 191, 36, 0.7)) drop-shadow(0 0 8px rgba(236, 72, 153, 0.6));
  animation: roseSwing 6s ease-in-out infinite;
  opacity: 0.85;
}

.hero-rose-tl { top: 8%; left: 4%; animation-delay: 0s; }
.hero-rose-tr { top: 12%; right: 4%; animation-delay: -1.5s; transform: scaleX(-1); }
.hero-rose-bl { bottom: 18%; left: 5%; animation-delay: -3s; font-size: clamp(1.5rem, 3vw, 2.2rem); color: #ec4899; }
.hero-rose-br { bottom: 22%; right: 5%; animation-delay: -4.5s; font-size: clamp(1.5rem, 3vw, 2.2rem); color: #ec4899; }

@keyframes roseSwing {
  0%, 100% { transform: rotate(-8deg) translateY(0); }
  50% { transform: rotate(8deg) translateY(-12px); }
}

.hero-rose-tr { transform: scaleX(-1) rotate(-8deg); }
.hero-rose-tr { animation-name: roseSwingFlip; }

@keyframes roseSwingFlip {
  0%, 100% { transform: scaleX(-1) rotate(-8deg) translateY(0); }
  50% { transform: scaleX(-1) rotate(8deg) translateY(-12px); }
}

.brand-bk {
  width: 38px;
  height: 38px;
  filter: drop-shadow(0 2px 6px rgba(13, 78, 184, 0.3));
}

.brand-divider {
  width: 1px;
  height: 36px;
  background: linear-gradient(to bottom, transparent, var(--border), transparent);
}

.brand-meta { margin-left: auto; display: flex; gap: 8px; align-items: center; }

.badge-bk {
  background: linear-gradient(135deg, var(--c-bk), var(--c-bk-light));
  color: white;
  padding: 6px 14px;
  border-radius: 999px;
  font-weight: 700;
  font-size: 0.8rem;
  letter-spacing: 0.05em;
  box-shadow: 0 2px 8px rgba(13, 78, 184, 0.3);
}

/* Section title now uses rose gradient */
.section-title {
  font-size: clamp(1.5rem, 3vw, 2.4rem);
  font-weight: 900;
  margin-bottom: 8px;
  background: var(--grad-rose);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  display: inline-block;
  filter: drop-shadow(0 2px 8px rgba(236, 72, 153, 0.25));
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: var(--bg-card);
  backdrop-filter: blur(12px);
  border: 1.5px solid var(--border);
  padding: 8px 18px;
  border-radius: 999px;
  font-weight: 600;
  font-size: 0.9rem;
  color: var(--c-purple);
  box-shadow: var(--shadow-sm);
  margin-bottom: 24px;
  animation: floatY 3s ease-in-out infinite;
}

@keyframes floatY {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-8px); }
}

.hero h1 {
  font-size: clamp(2.4rem, 8vw, 6rem);
  font-weight: 900;
  line-height: 1.05;
  letter-spacing: -0.03em;
  margin-bottom: 24px;
  background: var(--grad-hero);
  background-size: 300% 300%;
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  animation: gradientShift 6s ease infinite;
  filter: drop-shadow(0 6px 24px rgba(236, 72, 153, 0.45));
}

@keyframes gradientShift {
  0%, 100% { background-position: 0% 50%; }
  50% { background-position: 100% 50%; }
}

.hero h1 .lightning {
  display: inline-block;
  animation: zap 2.5s ease-in-out infinite;
  filter: drop-shadow(0 0 20px var(--c-yellow));
}

@keyframes zap {
  0%, 100% { transform: rotate(0deg) scale(1); }
  10% { transform: rotate(-10deg) scale(1.1); }
  20% { transform: rotate(10deg) scale(1.15); }
  30% { transform: rotate(0deg) scale(1); }
}

.hero-subtitle {
  font-size: clamp(1rem, 2.5vw, 1.4rem);
  color: var(--text-muted);
  margin-bottom: 32px;
  max-width: 720px;
  font-weight: 500;
}

.hero-author {
  display: inline-block;
  font-weight: 700;
  background: var(--grad-button);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-cta {
  display: flex;
  flex-wrap: wrap;
  gap: 14px;
  justify-content: center;
  margin-bottom: 40px;
}

.hero-stats {
  display: flex;
  flex-wrap: wrap;
  gap: 24px;
  justify-content: center;
  margin-top: 16px;
}

.stat {
  background: var(--bg-card);
  backdrop-filter: blur(12px);
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  padding: 16px 24px;
  min-width: 130px;
  box-shadow: var(--shadow-sm);
  transition: all 0.3s;
}

.stat:hover {
  transform: translateY(-6px) scale(1.05);
  box-shadow: var(--shadow-md);
}

.stat-num {
  font-size: 2rem;
  font-weight: 900;
  background: var(--grad-button);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  line-height: 1;
}

.stat-label {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-top: 4px;
  font-weight: 500;
}

.hero-scroll {
  position: absolute;
  bottom: 50px;
  left: 50%;
  transform: translateX(-50%);
  color: var(--c-purple);
  font-size: 1.5rem;
  animation: bounce 2s ease-in-out infinite;
}

.hero-secret {
  position: absolute;
  bottom: 18px;
  left: 50%;
  transform: translateX(-50%);
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-size: 0.92rem;
  color: var(--c-pink-deep);
  font-weight: 600;
  font-style: italic;
  letter-spacing: 0.04em;
  background: rgba(255, 255, 255, 0.7);
  backdrop-filter: blur(12px);
  border: 1.5px solid rgba(236, 72, 153, 0.3);
  padding: 10px 22px;
  border-radius: 999px;
  box-shadow: 0 4px 20px rgba(236, 72, 153, 0.25);
  transition: all 0.4s;
  text-align: center;
  max-width: 90vw;
  white-space: nowrap;
}

.hero-secret em {
  font-style: italic;
  font-weight: 800;
  background: var(--grad-rose);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-secret:hover {
  background: rgba(255, 240, 245, 0.95);
  transform: translateX(-50%) translateY(-4px) scale(1.05);
  box-shadow: 0 8px 30px rgba(236, 72, 153, 0.4);
}

.rose-icon {
  display: inline-block;
  font-size: 1.2rem;
  filter: drop-shadow(0 0 8px rgba(251, 191, 36, 0.9)) drop-shadow(0 0 4px rgba(236, 72, 153, 0.7));
  animation: roseGlow 3s ease-in-out infinite;
}

.rose-icon:nth-child(3) { animation-delay: -2s; }

@keyframes roseGlow {
  0%, 100% { transform: rotate(-5deg) scale(1); filter: drop-shadow(0 0 6px rgba(251, 191, 36, 0.7)); }
  50% { transform: rotate(5deg) scale(1.15); filter: drop-shadow(0 0 14px rgba(255, 110, 199, 0.9)); }
}

@keyframes bounce {
  0%, 100% { transform: translateX(-50%) translateY(0); }
  50% { transform: translateX(-50%) translateY(10px); }
}

/* ============================================
   🧭 STICKY HEADER (sub pages)
   ============================================ */
.site-header {
  background: rgba(255, 255, 255, 0.7);
  backdrop-filter: blur(20px) saturate(180%);
  -webkit-backdrop-filter: blur(20px) saturate(180%);
  border-bottom: 1px solid var(--border);
  padding: 14px 20px;
  position: sticky;
  top: 0;
  z-index: 50;
  box-shadow: var(--shadow-sm);
}

.site-header-inner {
  width: 100%;
  margin: 0;
  padding: 0 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  flex-wrap: wrap;
}

@media (min-width: 1200px) {
  .site-header-inner { padding: 0 56px; }
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: var(--text);
}

.brand-logo {
  width: 40px;
  height: 40px;
  display: grid;
  place-items: center;
  background: var(--grad-button);
  border-radius: 10px;
  font-size: 1.4rem;
  box-shadow: var(--shadow-glow);
  animation: pulse 3s ease-in-out infinite;
}

@keyframes pulse {
  0%, 100% { box-shadow: 0 0 20px rgba(255, 110, 199, 0.5); }
  50% { box-shadow: 0 0 40px rgba(168, 85, 247, 0.7); }
}

.brand-name {
  font-weight: 800;
  font-size: 1.05rem;
  background: var(--grad-button);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.brand-sub {
  font-size: 0.78rem;
  color: var(--text-muted);
  font-weight: 500;
}

/* ============================================
   📑 TAB NAVIGATION
   ============================================ */
.tabs {
  position: sticky;
  top: 70px;
  z-index: 40;
  background: rgba(255, 255, 255, 0.85);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border);
  padding: 0;
  box-shadow: var(--shadow-sm);
}

.tabs-inner {
  width: 100%;
  margin: 0;
  display: flex;
  gap: 4px;
  overflow-x: auto;
  scrollbar-width: thin;
  padding: 8px 24px;
}

@media (min-width: 1200px) {
  .tabs-inner { padding: 8px 56px; }
}

.tabs-inner::-webkit-scrollbar { height: 4px; }
.tabs-inner::-webkit-scrollbar-thumb { background: var(--c-purple); border-radius: 4px; }

.tab-btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 18px;
  background: transparent;
  border: none;
  border-radius: 10px;
  font-weight: 600;
  font-size: 0.95rem;
  color: var(--text-muted);
  cursor: pointer;
  white-space: nowrap;
  transition: all 0.25s;
  text-decoration: none;
  min-height: 44px;
}

.tab-btn:hover {
  background: rgba(168, 85, 247, 0.08);
  color: var(--c-purple);
  transform: translateY(-2px);
}

.tab-btn.is-active {
  background: var(--grad-button);
  color: white;
  box-shadow: var(--shadow-md);
}

.tab-content {
  display: none;
  animation: fadeUp 0.4s ease;
}

.tab-content.is-active {
  display: block;
}

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}

/* ============================================
   📦 MAIN CONTAINER
   ============================================ */
main {
  width: 100%;
  margin: 0;
  padding: 32px 32px 80px;
}

@media (min-width: 1200px) {
  main { padding: 40px 56px 100px; }
}

@media (min-width: 1600px) {
  main { padding: 48px 80px 120px; }
}

.section-title {
  font-size: clamp(1.5rem, 3vw, 2.2rem);
  font-weight: 800;
  margin-bottom: 8px;
  background: var(--grad-button);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  display: inline-block;
}

.section-desc {
  color: var(--text-muted);
  margin-bottom: 28px;
  font-size: 1rem;
}

/* ============================================
   📚 LÝ THUYẾT - CHAPTERS
   ============================================ */
.toc {
  display: grid;
  grid-template-columns: 1fr;
  gap: 24px;
}

@media (min-width: 768px) { .toc { grid-template-columns: repeat(2, 1fr); } }
@media (min-width: 1400px) { .toc { grid-template-columns: repeat(4, 1fr); } }

.chapter {
  background: var(--bg-card);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-radius: var(--radius);
  padding: 28px;
  border: 1.5px solid var(--border);
  box-shadow: var(--shadow-md);
  position: relative;
  overflow: hidden;
  transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

.chapter::before {
  content: '';
  position: absolute;
  inset: 0;
  background: var(--grad-card);
  opacity: 0.4;
  z-index: -1;
}

.chapter:nth-child(1) { --accent: var(--c-pink); }
.chapter:nth-child(2) { --accent: var(--c-purple); }
.chapter:nth-child(3) { --accent: var(--c-cyan); }
.chapter:nth-child(4) { --accent: var(--c-orange); }

.chapter:hover {
  transform: translateY(-6px);
  box-shadow: var(--shadow-lg);
}

.chapter h2 {
  font-size: 1.5rem;
  font-weight: 800;
  margin-bottom: 20px;
  display: flex;
  align-items: center;
  gap: 12px;
}

.chapter-num {
  width: 44px;
  height: 44px;
  display: grid;
  place-items: center;
  background: var(--accent);
  color: white;
  border-radius: 12px;
  font-weight: 900;
  font-size: 1.3rem;
  box-shadow: 0 4px 16px color-mix(in srgb, var(--accent) 50%, transparent);
}

.section-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.section-link {
  display: flex;
  align-items: flex-start;
  gap: 12px;
  padding: 14px 16px;
  background: var(--bg-card-solid);
  border: 1.5px solid transparent;
  border-radius: var(--radius-sm);
  text-decoration: none;
  color: var(--text);
  transition: all 0.25s;
  min-height: 44px;
  position: relative;
  overflow: hidden;
}

.section-link::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  bottom: 0;
  width: 4px;
  background: var(--accent);
  transform: scaleY(0);
  transform-origin: top;
  transition: transform 0.25s;
}

.section-link:hover,
.section-link:focus {
  border-color: var(--accent);
  transform: translateX(6px);
  box-shadow: var(--shadow-sm);
}

.section-link:hover::before,
.section-link:focus::before {
  transform: scaleY(1);
}

.section-num {
  display: grid;
  place-items: center;
  min-width: 32px;
  height: 32px;
  background: color-mix(in srgb, var(--accent) 15%, transparent);
  color: var(--accent);
  font-weight: 800;
  border-radius: 8px;
  font-size: 0.85rem;
}

.section-info { flex: 1; min-width: 0; }

.section-title-text {
  font-weight: 600;
  font-size: 0.98rem;
  display: block;
}

.section-annotation {
  display: block;
  margin-top: 4px;
  font-size: 0.85rem;
  color: var(--c-orange);
  font-style: italic;
  font-weight: 600;
}

.indicators {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: 8px;
}

.indicator {
  display: inline-flex;
  align-items: center;
  font-size: 0.72rem;
  padding: 3px 8px;
  border-radius: 6px;
  font-weight: 600;
  background: color-mix(in srgb, var(--accent) 12%, transparent);
  color: var(--accent);
}

.indicator.is-missing { display: none; }

/* ============================================
   📋 CARD GROUPS (Đề thi, HW, Quiz, Sách, Lab)
   ============================================ */
.group-section {
  margin-bottom: 40px;
}

.group-header {
  font-size: 1.4rem;
  font-weight: 800;
  margin-bottom: 16px;
  padding: 12px 20px;
  background: var(--grad-button-pink);
  color: white;
  border-radius: var(--radius);
  display: inline-block;
  box-shadow: var(--shadow-md);
}

.group-header.is-final { background: var(--grad-button); }
.group-header.is-special {
  background: var(--grad-button-yellow);
  animation: glowSpecial 2s ease-in-out infinite;
}

@keyframes glowSpecial {
  0%, 100% { box-shadow: 0 0 20px rgba(251, 191, 36, 0.5); }
  50% { box-shadow: 0 0 40px rgba(251, 146, 60, 0.7); }
}

.group-note {
  background: linear-gradient(135deg, rgba(251, 191, 36, 0.15), rgba(255, 110, 199, 0.1));
  border-left: 4px solid var(--c-yellow);
  padding: 14px 18px;
  border-radius: var(--radius-sm);
  margin-bottom: 16px;
  color: var(--text);
  font-size: 0.95rem;
  font-weight: 500;
}

.group-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 16px;
}

@media (min-width: 600px) { .group-grid { grid-template-columns: repeat(2, 1fr); } }
@media (min-width: 1000px) { .group-grid { grid-template-columns: repeat(3, 1fr); } }
@media (min-width: 1300px) { .group-grid { grid-template-columns: repeat(4, 1fr); } }
@media (min-width: 1600px) { .group-grid { grid-template-columns: repeat(5, 1fr); } }
@media (min-width: 2000px) { .group-grid { grid-template-columns: repeat(6, 1fr); } }

.file-card {
  background: var(--bg-card-solid);
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  padding: 16px;
  text-decoration: none;
  color: var(--text);
  display: flex;
  flex-direction: column;
  gap: 8px;
  transition: all 0.3s;
  min-height: 100px;
  position: relative;
  overflow: hidden;
}

.file-card::before {
  content: '';
  position: absolute;
  top: -50%;
  left: -50%;
  width: 200%;
  height: 200%;
  background: var(--grad-button-pink);
  opacity: 0;
  transition: opacity 0.3s;
  z-index: 0;
}

.file-card > * { position: relative; z-index: 1; }

.file-card:hover {
  transform: translateY(-4px) scale(1.02);
  box-shadow: var(--shadow-lg);
  border-color: var(--c-pink);
}

.file-icon {
  display: inline-grid;
  place-items: center;
  width: 40px;
  height: 40px;
  background: var(--grad-button-pink);
  color: white;
  border-radius: 10px;
  font-size: 1.2rem;
  flex-shrink: 0;
  box-shadow: var(--shadow-sm);
}

.file-icon.is-pdf { background: var(--grad-button-pink); }
.file-icon.is-video { background: linear-gradient(135deg, #ef4444, #f59e0b); }
.file-icon.is-solution { background: var(--grad-button-green); }
.file-icon.is-book { background: var(--grad-button); }

.file-title {
  font-weight: 700;
  font-size: 0.95rem;
  line-height: 1.3;
}

.file-name {
  font-size: 0.78rem;
  color: var(--text-muted);
  word-break: break-word;
}

.file-status {
  margin-top: auto;
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--c-cyan);
  display: inline-flex;
  align-items: center;
  gap: 4px;
}

.file-status.is-missing {
  color: var(--c-orange);
}

/* ============================================
   📅 HOMEWORK TABLE
   ============================================ */
.hw-card {
  background: var(--bg-card-solid);
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  margin-bottom: 20px;
  box-shadow: var(--shadow-sm);
  transition: all 0.3s;
}

.hw-card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.hw-title {
  font-size: 1.4rem;
  font-weight: 800;
  background: var(--grad-button);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: 16px;
  display: flex;
  align-items: center;
  gap: 10px;
}

.hw-title-num {
  background: var(--grad-button);
  color: white;
  -webkit-text-fill-color: white;
  width: 36px;
  height: 36px;
  display: grid;
  place-items: center;
  border-radius: 10px;
  font-weight: 900;
}

.hw-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 12px;
}

@media (min-width: 768px) {
  .hw-grid { grid-template-columns: repeat(2, 1fr); }
}

.hw-block {
  background: var(--bg-soft);
  border-radius: var(--radius-sm);
  padding: 14px 16px;
  border-left: 4px solid var(--c-pink);
}

.hw-block.is-hk242 { border-left-color: var(--c-purple); }
.hw-block.is-solution { border-left-color: var(--c-green); }
.hw-block.is-video { border-left-color: var(--c-red); }

.hw-block-label {
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 6px;
}

.hw-block-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  color: var(--c-purple);
  text-decoration: none;
  font-weight: 600;
  font-size: 0.95rem;
  transition: all 0.2s;
}

.hw-block-link:hover {
  color: var(--c-pink);
  transform: translateX(2px);
}

/* ============================================
   📝 QUIZ
   ============================================ */
.quiz-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 20px;
}

@media (min-width: 1000px) { .quiz-grid { grid-template-columns: repeat(2, 1fr); } }
@media (min-width: 1500px) { .quiz-grid { grid-template-columns: repeat(3, 1fr); } }

.quiz-card {
  background: var(--bg-card-solid);
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  padding: 22px;
  box-shadow: var(--shadow-sm);
  transition: all 0.3s;
}

.quiz-card:hover {
  box-shadow: var(--shadow-md);
}

.quiz-card.is-special {
  background: linear-gradient(135deg, #fff5e6, #ffe4f1);
  border: 2px solid var(--c-yellow);
  box-shadow: 0 0 0 4px rgba(251, 191, 36, 0.1), var(--shadow-md);
}

.quiz-card-title {
  font-size: 1.15rem;
  font-weight: 800;
  color: var(--text);
  margin-bottom: 14px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.quiz-card.is-special .quiz-card-title {
  color: var(--c-orange);
}

.problem-row {
  background: var(--bg-soft);
  border-radius: var(--radius-sm);
  padding: 12px 14px;
  margin-bottom: 10px;
}

.problem-row:last-child { margin-bottom: 0; }

.problem-name {
  font-weight: 700;
  font-size: 0.95rem;
  margin-bottom: 4px;
  color: var(--text);
}

.problem-note {
  font-size: 0.82rem;
  color: var(--c-red);
  font-style: italic;
  margin: 4px 0 8px;
  font-weight: 500;
}

.problem-links {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 6px;
}

.btn-link {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 6px 12px;
  background: white;
  border: 1.5px solid var(--border);
  border-radius: 8px;
  text-decoration: none;
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--text);
  transition: all 0.2s;
  min-height: 32px;
}

.btn-link:hover {
  border-color: var(--c-purple);
  background: rgba(168, 85, 247, 0.08);
  transform: translateY(-1px);
}

.btn-link.is-pdf { color: var(--c-purple); }
.btn-link.is-solution { color: var(--c-green); border-color: rgba(16, 185, 129, 0.3); }
.btn-link.is-video { color: var(--c-red); border-color: rgba(239, 68, 68, 0.3); }

/* ============================================
   🔘 BUTTONS
   ============================================ */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 24px;
  border-radius: 12px;
  text-decoration: none;
  font-weight: 700;
  font-size: 0.95rem;
  border: none;
  cursor: pointer;
  transition: all 0.25s;
  min-height: 44px;
  position: relative;
  overflow: hidden;
}

.btn-hero {
  background: var(--grad-button);
  color: white;
  font-size: 1.05rem;
  padding: 16px 32px;
  border-radius: 14px;
  box-shadow: var(--shadow-glow);
}

.btn-hero:hover {
  transform: translateY(-3px) scale(1.05);
  box-shadow: 0 0 60px rgba(255, 110, 199, 0.6);
}

.btn-hero-outline {
  background: var(--bg-card);
  backdrop-filter: blur(12px);
  color: var(--c-purple);
  border: 2px solid var(--c-purple);
  font-size: 1.05rem;
  padding: 14px 30px;
  border-radius: 14px;
}

.btn-hero-outline:hover {
  background: var(--c-purple);
  color: white;
  transform: translateY(-3px);
}

.btn-primary {
  background: var(--grad-button);
  color: white;
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.btn-secondary {
  background: white;
  color: var(--c-purple);
  border: 1.5px solid var(--c-purple);
}

.btn-secondary:hover {
  background: var(--c-purple);
  color: white;
}

/* ============================================
   📄 SECTION DETAIL
   ============================================ */
.section-meta {
  display: inline-block;
  background: var(--grad-button);
  color: white;
  padding: 6px 14px;
  border-radius: 999px;
  font-size: 0.85rem;
  font-weight: 700;
  margin-bottom: 12px;
}

.section-detail-title {
  font-size: clamp(1.6rem, 4vw, 2.4rem);
  font-weight: 800;
  line-height: 1.2;
  margin-bottom: 24px;
}

.section-detail-annotation {
  display: block;
  font-size: 1.05rem;
  color: var(--c-orange);
  font-weight: 600;
  margin-top: 8px;
  font-style: italic;
}

.doc-block {
  background: var(--bg-card-solid);
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  margin-bottom: 20px;
  box-shadow: var(--shadow-sm);
  transition: all 0.3s;
}

.doc-block:hover {
  box-shadow: var(--shadow-md);
}

.doc-block h3 {
  font-size: 1.2rem;
  font-weight: 800;
  margin-bottom: 12px;
  background: var(--grad-button);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.doc-block .filename {
  font-size: 0.88rem;
  color: var(--text-muted);
  margin-bottom: 14px;
  word-break: break-word;
  display: block;
}

.pdf-frame {
  width: 100%;
  height: clamp(400px, 70vh, 800px);
  border: 1.5px solid var(--border);
  border-radius: 12px;
  background: white;
}

.pdf-actions, .video-list {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 14px;
}

.placeholder-msg {
  padding: 16px;
  background: linear-gradient(135deg, rgba(251, 191, 36, 0.15), rgba(255, 110, 199, 0.1));
  border-left: 4px solid var(--c-yellow);
  border-radius: var(--radius-sm);
  color: var(--text);
  font-size: 0.95rem;
  font-weight: 500;
}

.section-nav {
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 32px;
  padding-top: 24px;
  border-top: 1.5px solid var(--border);
}

.section-nav .btn {
  flex: 1;
  min-width: 140px;
  max-width: 280px;
}

.nav-spacer { flex: 1; min-width: 140px; }

/* ============================================
   🎨 LOADING / ERROR / 404
   ============================================ */
.loading {
  text-align: center;
  padding: 80px 20px;
  color: var(--text-muted);
}

.loading::before {
  content: '⚡';
  display: inline-block;
  font-size: 3rem;
  animation: zap 1.5s ease-in-out infinite;
}

.error-banner {
  background: linear-gradient(135deg, rgba(239, 68, 68, 0.15), rgba(251, 146, 60, 0.1));
  border: 1.5px solid var(--c-red);
  color: var(--c-red);
  padding: 18px 22px;
  border-radius: var(--radius);
  margin-bottom: 20px;
  font-weight: 600;
}

.not-found {
  text-align: center;
  padding: 80px 20px;
}

.not-found-emoji {
  font-size: 6rem;
  animation: floatY 3s ease-in-out infinite;
  margin-bottom: 16px;
}

.not-found h2 {
  font-size: clamp(1.8rem, 4vw, 3rem);
  font-weight: 900;
  background: var(--grad-button);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: 16px;
}

/* ============================================
   👣 FOOTER
   ============================================ */
.site-footer {
  text-align: center;
  padding: 40px 20px;
  color: var(--text-muted);
  border-top: 1px solid var(--border);
  margin-top: 60px;
  background: rgba(255, 255, 255, 0.5);
  backdrop-filter: blur(12px);
}

.footer-secret {
  margin-top: 16px;
  font-size: 0.78rem;
  font-style: italic;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  opacity: 0.6;
  letter-spacing: 0.05em;
}

.footer-rose {
  color: #ff6ec7;
  font-size: 0.9rem;
  filter: drop-shadow(0 0 4px rgba(251, 191, 36, 0.6));
  animation: roseGlow 5s ease-in-out infinite;
}

.site-footer-emoji {
  font-size: 1.5rem;
  margin-bottom: 8px;
}

/* ============================================
   ✨ Scroll reveal animation
   ============================================ */
.reveal {
  opacity: 0;
  transform: translateY(20px);
  transition: all 0.6s cubic-bezier(0.4, 0, 0.2, 1);
}

.reveal.is-visible {
  opacity: 1;
  transform: translateY(0);
}

/* Mobile tweaks */
@media (max-width: 600px) {
  .hero { padding: 60px 16px 100px; }
  .hero-stats { gap: 10px; }
  .stat { padding: 12px 16px; min-width: 100px; }
  .stat-num { font-size: 1.5rem; }
  .tabs-inner { padding: 8px; }
  .tab-btn { padding: 8px 14px; font-size: 0.88rem; }
  .chapter { padding: 20px; }
  .group-grid { grid-template-columns: 1fr; }
}