/* ============================================
   VIỆT NĂNG — Premium Landing Page
   Design: Dark hero + Warm amber/gold palette
   ============================================ */

/* --- Google Fonts --- */
@import url('https://fonts.googleapis.com/css2?family=Be+Vietnam+Pro:wght@300;400;500;600;700;800;900&display=swap');

/* --- Design Tokens --- */
:root {
  --font: 'Be Vietnam Pro', -apple-system, sans-serif;

  /* Brand: Warm amber/gold → energy + petroleum */
  --brand-50: #fffbeb;
  --brand-100: #fef3c7;
  --brand-200: #fde68a;
  --brand-300: #fcd34d;
  --brand-400: #fbbf24;
  --brand-500: #f59e0b;
  --brand-600: #d97706;
  --brand-700: #b45309;
  --brand-800: #92400e;
  --brand-900: #78350f;

  /* Accents */
  --fire-500: #ef4444;
  --fire-600: #dc2626;
  --teal-400: #2dd4bf;
  --teal-500: #14b8a6;

  /* Neutrals */
  --slate-50: #f8fafc;
  --slate-100: #f1f5f9;
  --slate-200: #e2e8f0;
  --slate-300: #cbd5e1;
  --slate-400: #94a3b8;
  --slate-500: #64748b;
  --slate-600: #475569;
  --slate-700: #334155;
  --slate-800: #1e293b;
  --slate-900: #0f172a;
  --slate-950: #020617;

  /* Surfaces */
  --bg: #ffffff;
  --bg-alt: #f8fafc;
  --bg-dark: #0f172a;
  --text: #1e293b;
  --text-secondary: #475569;
  --text-muted: #94a3b8;
  --text-on-dark: #f1f5f9;

  /* Spacing */
  --section-py: 96px;
  --container-max: 1200px;
  --radius: 16px;
  --radius-sm: 10px;

  /* Shadows */
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.06);
  --shadow-md: 0 4px 20px rgba(0,0,0,0.08);
  --shadow-lg: 0 12px 40px rgba(0,0,0,0.12);
  --shadow-glow: 0 0 40px rgba(245,158,11,0.15);

  /* Transitions */
  --ease: cubic-bezier(0.4, 0, 0.2, 1);
}

/* --- Reset & Base --- */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; font-size: 16px; }

body {
  font-family: var(--font);
  color: var(--text);
  background: var(--bg);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  overflow-x: hidden;
}

img { max-width: 100%; height: auto; display: block; }
a { text-decoration: none; color: inherit; transition: color 0.3s var(--ease); }

.container {
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 24px;
}

/* --- Scroll Progress --- */
.scroll-progress {
  position: fixed;
  top: 0;
  left: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--brand-500), var(--brand-300));
  z-index: 9999;
  width: 0;
  transition: width 0.1s;
}

/* --- Top Bar --- */
.top-bar {
  background: var(--slate-900);
  color: var(--slate-300);
  font-size: 13px;
  padding: 8px 0;
  border-bottom: 1px solid rgba(255,255,255,0.06);
}
.top-bar .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 8px;
}
.top-bar-left { display: flex; gap: 20px; align-items: center; }
.top-bar-left span { display: flex; align-items: center; gap: 6px; }
.top-bar-right { display: flex; gap: 12px; align-items: center; }
.top-bar-right a {
  color: var(--slate-400);
  transition: color 0.3s, transform 0.3s;
}
.top-bar-right a:hover { color: var(--brand-400); transform: translateY(-1px); }

/* --- Header --- */
.header {
  background: var(--slate-900);
  padding: 16px 0;
  position: relative;
  z-index: 100;
}
.logo {
  display: flex;
  align-items: center;
  gap: 14px;
}
.logo img {
  width: 52px;
  height: 52px;
  border-radius: 12px;
  object-fit: contain;
  background: rgba(255,255,255,0.05);
  padding: 4px;
}
.logo-text h1 {
  font-size: 22px;
  font-weight: 800;
  color: var(--brand-400);
  letter-spacing: 2px;
  line-height: 1.2;
}
.logo-text span {
  font-size: 12px;
  color: var(--slate-400);
  letter-spacing: 0.5px;
}

/* --- Navigation --- */
.nav {
  background: var(--slate-800);
  position: sticky;
  top: 0;
  z-index: 999;
  box-shadow: 0 2px 20px rgba(0,0,0,0.3);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
}
.nav .container { display: flex; align-items: center; justify-content: center; }
.nav-toggle {
  display: none;
  background: none;
  border: none;
  color: var(--brand-400);
  font-size: 24px;
  cursor: pointer;
  padding: 12px;
}
.nav-list {
  list-style: none;
  display: flex;
  gap: 0;
}
.nav-list a {
  display: block;
  padding: 16px 20px;
  color: var(--slate-300);
  font-size: 14px;
  font-weight: 500;
  letter-spacing: 0.3px;
  position: relative;
  transition: color 0.3s var(--ease);
}
.nav-list a::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 50%;
  transform: translateX(-50%) scaleX(0);
  width: 60%;
  height: 2px;
  background: var(--brand-400);
  transition: transform 0.3s var(--ease);
}
.nav-list a:hover { color: var(--brand-400); }
.nav-list a:hover::after { transform: translateX(-50%) scaleX(1); }

/* --- Hero --- */
.hero {
  position: relative;
  height: 560px;
  overflow: hidden;
  background: var(--slate-950);
}
.hero-slider {
  position: absolute;
  inset: 0;
}
.hero-slide {
  position: absolute;
  inset: 0;
  opacity: 0;
  transition: opacity 1.2s ease;
}
.hero-slide.active { opacity: 1; }
.hero-slide img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  filter: brightness(0.4) saturate(1.1);
}
.hero-overlay {
  position: absolute;
  inset: 0;
  background: linear-gradient(135deg, rgba(15,23,42,0.85) 0%, rgba(15,23,42,0.5) 50%, rgba(245,158,11,0.15) 100%);
  display: flex;
  align-items: center;
  z-index: 2;
}
.hero-content {
  max-width: 640px;
  padding: 0 48px;
  animation: heroFadeIn 1.2s var(--ease);
}
@keyframes heroFadeIn {
  from { opacity: 0; transform: translateY(30px); }
  to { opacity: 1; transform: translateY(0); }
}
.hero-badge {
  display: inline-block;
  background: rgba(245,158,11,0.15);
  color: var(--brand-400);
  padding: 6px 16px;
  border-radius: 24px;
  font-size: 13px;
  font-weight: 600;
  letter-spacing: 0.5px;
  border: 1px solid rgba(245,158,11,0.3);
  margin-bottom: 20px;
  backdrop-filter: blur(8px);
}
.hero-content h2 {
  font-size: clamp(32px, 5vw, 48px);
  font-weight: 800;
  color: #fff;
  line-height: 1.15;
  margin-bottom: 16px;
  text-shadow: 0 2px 20px rgba(0,0,0,0.3);
}
.hero-content p {
  font-size: 17px;
  color: var(--slate-300);
  margin-bottom: 28px;
  line-height: 1.8;
}

/* --- Buttons --- */
.hero-buttons { display: flex; gap: 14px; flex-wrap: wrap; }
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 14px 32px;
  border-radius: 10px;
  font-size: 15px;
  font-weight: 600;
  letter-spacing: 0.3px;
  cursor: pointer;
  border: none;
  transition: all 0.35s var(--ease);
}
.btn-white {
  background: var(--brand-500);
  color: #fff;
  box-shadow: 0 4px 16px rgba(245,158,11,0.3);
}
.btn-white:hover {
  background: var(--brand-600);
  transform: translateY(-2px);
  box-shadow: 0 6px 24px rgba(245,158,11,0.4);
}
.btn-outline {
  background: transparent;
  color: #fff;
  border: 2px solid rgba(255,255,255,0.3);
}
.btn-outline:hover {
  border-color: var(--brand-400);
  color: var(--brand-400);
  transform: translateY(-2px);
}

/* --- Stats Bar --- */
.stats-bar {
  background: var(--slate-900);
  padding: 0;
  position: relative;
  z-index: 3;
  border-bottom: 1px solid rgba(255,255,255,0.05);
}
.stats-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
}
.stat-item {
  text-align: center;
  padding: 32px 16px;
  position: relative;
  transition: background 0.3s;
}
.stat-item:not(:last-child)::after {
  content: '';
  position: absolute;
  right: 0;
  top: 25%;
  height: 50%;
  width: 1px;
  background: rgba(255,255,255,0.08);
}
.stat-item:hover { background: rgba(245,158,11,0.05); }
.stat-number {
  display: block;
  font-size: 32px;
  font-weight: 800;
  color: var(--brand-400);
  line-height: 1.2;
  margin-bottom: 6px;
}
.stat-label {
  font-size: 13px;
  color: var(--slate-400);
  font-weight: 500;
}

/* --- Section --- */
.section {
  padding: var(--section-py) 0;
}
.section-alt {
  background: var(--bg-alt);
}
.section-header {
  text-align: center;
  max-width: 600px;
  margin: 0 auto 56px;
}
.section-header h2 {
  font-size: 36px;
  font-weight: 800;
  color: var(--text);
  margin-bottom: 14px;
  position: relative;
}
.section-header h2::after {
  content: '';
  display: block;
  width: 48px;
  height: 3px;
  background: linear-gradient(90deg, var(--brand-500), var(--brand-300));
  margin: 16px auto 0;
  border-radius: 2px;
}
.section-header p {
  font-size: 16px;
  color: var(--text-secondary);
  line-height: 1.7;
}

/* --- About --- */
.about-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 56px;
  align-items: center;
}
.about-image img {
  border-radius: var(--radius);
  box-shadow: var(--shadow-lg);
  transition: transform 0.5s var(--ease);
}
.about-image:hover img { transform: scale(1.02); }
.about-text h3 {
  font-size: 32px;
  font-weight: 800;
  margin-bottom: 20px;
  color: var(--text);
}
.highlight { color: var(--brand-600); }
.about-text p {
  font-size: 15px;
  color: var(--text-secondary);
  margin-bottom: 16px;
  line-height: 1.8;
}
.about-features {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin-top: 24px;
}
.about-feature {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 14px;
  font-weight: 500;
  color: var(--text);
  padding: 10px 14px;
  background: var(--brand-50);
  border-radius: var(--radius-sm);
  border: 1px solid var(--brand-100);
  transition: all 0.3s var(--ease);
}
.about-feature:hover {
  background: var(--brand-100);
  transform: translateX(4px);
}
.about-feature .icon {
  color: var(--brand-600);
  font-weight: 800;
  font-size: 16px;
}

/* --- Course Cards --- */
.courses-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 28px;
}
.course-card {
  background: #fff;
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--slate-200);
  transition: all 0.4s var(--ease);
  position: relative;
}
.course-card:hover {
  transform: translateY(-6px);
  box-shadow: var(--shadow-lg);
  border-color: var(--brand-200);
}
.course-card-badge {
  position: absolute;
  top: 16px;
  right: 16px;
  background: var(--brand-500);
  color: #fff;
  padding: 4px 12px;
  border-radius: 20px;
  font-size: 12px;
  font-weight: 700;
  z-index: 2;
  letter-spacing: 0.5px;
}
.course-image {
  height: 200px;
  overflow: hidden;
}
.course-image img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform 0.6s var(--ease);
}
.course-card:hover .course-image img { transform: scale(1.08); }
.course-body {
  padding: 24px;
}
.course-body h3 {
  font-size: 17px;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 10px;
  line-height: 1.4;
}
.course-body p {
  font-size: 14px;
  color: var(--text-secondary);
  line-height: 1.7;
  margin-bottom: 16px;
}
.course-meta {
  display: flex;
  align-items: center;
  gap: 16px;
  flex-wrap: wrap;
}
.course-meta-item {
  display: flex;
  align-items: center;
  gap: 5px;
  font-size: 13px;
  color: var(--text-muted);
  font-weight: 500;
}
.course-meta-item .icon { font-size: 14px; }
.course-price {
  margin-left: auto;
  font-size: 14px;
  font-weight: 700;
  color: var(--brand-600);
  background: var(--brand-50);
  padding: 4px 12px;
  border-radius: 6px;
}

/* --- Why Grid --- */
.why-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 24px;
}
.why-card {
  background: #fff;
  border-radius: var(--radius);
  padding: 32px 24px;
  text-align: center;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--slate-200);
  transition: all 0.4s var(--ease);
  position: relative;
  overflow: hidden;
}
.why-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--brand-500), var(--brand-300));
  transform: scaleX(0);
  transition: transform 0.4s var(--ease);
}
.why-card:hover::before { transform: scaleX(1); }
.why-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}
.why-icon {
  width: 56px;
  height: 56px;
  background: linear-gradient(135deg, var(--brand-50), var(--brand-100));
  border-radius: 14px;
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0 auto 20px;
  transition: all 0.3s var(--ease);
}
.why-icon svg {
  width: 28px;
  height: 28px;
  color: var(--brand-600);
}
.why-card:hover .why-icon {
  background: linear-gradient(135deg, var(--brand-500), var(--brand-400));
  transform: scale(1.1);
}
.why-card:hover .why-icon svg { color: #fff; }
.why-card h3 {
  font-size: 17px;
  font-weight: 700;
  margin-bottom: 10px;
  color: var(--text);
}
.why-card p {
  font-size: 14px;
  color: var(--text-secondary);
  line-height: 1.7;
}

/* --- CTA --- */
.cta {
  background: linear-gradient(135deg, var(--slate-900) 0%, var(--slate-800) 100%);
  padding: 72px 0;
  text-align: center;
  position: relative;
  overflow: hidden;
}
.cta::before {
  content: '';
  position: absolute;
  top: -50%;
  right: -20%;
  width: 400px;
  height: 400px;
  background: radial-gradient(circle, rgba(245,158,11,0.12), transparent 70%);
  border-radius: 50%;
  animation: ctaGlow 6s ease-in-out infinite alternate;
}
@keyframes ctaGlow {
  from { transform: translate(0, 0) scale(1); }
  to { transform: translate(-30px, 20px) scale(1.2); }
}
.cta h2 {
  font-size: 36px;
  font-weight: 800;
  color: #fff;
  margin-bottom: 14px;
  position: relative;
  z-index: 2;
}
.cta p {
  font-size: 17px;
  color: var(--slate-300);
  margin-bottom: 28px;
  max-width: 520px;
  margin-left: auto;
  margin-right: auto;
  position: relative;
  z-index: 2;
}

/* --- News Cards --- */
.news-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 28px;
}
.news-card {
  background: #fff;
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--slate-200);
  transition: all 0.4s var(--ease);
}
.news-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}
.news-image {
  position: relative;
  height: 200px;
  overflow: hidden;
}
.news-image img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform 0.6s var(--ease);
}
.news-card:hover .news-image img { transform: scale(1.06); }
.news-date {
  position: absolute;
  bottom: 12px;
  left: 12px;
  background: var(--brand-500);
  color: #fff;
  padding: 4px 12px;
  border-radius: 6px;
  font-size: 12px;
  font-weight: 600;
}
.news-body { padding: 24px; }
.news-tag {
  display: inline-block;
  background: var(--brand-50);
  color: var(--brand-700);
  padding: 3px 10px;
  border-radius: 5px;
  font-size: 12px;
  font-weight: 600;
  margin-bottom: 10px;
}
.news-body h3 {
  font-size: 16px;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 8px;
  line-height: 1.5;
}
.news-body p {
  font-size: 14px;
  color: var(--text-secondary);
  line-height: 1.7;
}

/* --- Footer --- */
.footer {
  background: var(--slate-900);
  color: var(--slate-300);
  padding: 64px 0 0;
}
.footer-grid {
  display: grid;
  grid-template-columns: 1.5fr 1fr 1fr 1.2fr;
  gap: 40px;
  padding-bottom: 48px;
  border-bottom: 1px solid rgba(255,255,255,0.06);
}
.footer-brand h3 {
  font-size: 22px;
  color: var(--brand-400);
  margin-bottom: 12px;
}
.footer-brand p {
  font-size: 14px;
  line-height: 1.7;
  color: var(--slate-400);
}
.footer h4 {
  font-size: 15px;
  font-weight: 700;
  color: #fff;
  margin-bottom: 16px;
  letter-spacing: 0.3px;
}
.footer-links {
  list-style: none;
}
.footer-links li { margin-bottom: 10px; }
.footer-links a {
  font-size: 14px;
  color: var(--slate-400);
  transition: color 0.3s, padding-left 0.3s;
}
.footer-links a:hover { color: var(--brand-400); padding-left: 4px; }
.footer-contact {
  list-style: none;
}
.footer-contact li {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  margin-bottom: 12px;
  font-size: 14px;
  color: var(--slate-400);
}
.footer-contact .icon { font-size: 16px; flex-shrink: 0; margin-top: 2px; }
.footer-bottom {
  text-align: center;
  padding: 24px 0;
  font-size: 13px;
  color: var(--slate-500);
}

/* --- Back to Top --- */
.back-to-top {
  position: fixed;
  bottom: 32px;
  right: 32px;
  width: 48px;
  height: 48px;
  background: var(--brand-500);
  color: #fff;
  border: none;
  border-radius: 14px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  visibility: hidden;
  transform: translateY(16px);
  transition: all 0.4s var(--ease);
  box-shadow: 0 4px 20px rgba(245,158,11,0.3);
  z-index: 999;
}
.back-to-top.visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}
.back-to-top:hover {
  background: var(--brand-600);
  transform: translateY(-3px);
}

/* --- Fade Animations --- */
.fade-in {
  opacity: 0;
  transform: translateY(24px);
  transition: opacity 0.7s var(--ease), transform 0.7s var(--ease);
}
.fade-in.visible {
  opacity: 1;
  transform: translateY(0);
}

/* --- Testimonial Cards (reusing why-card) --- */
.testimonial-card {
  background: #fff;
  border-radius: var(--radius);
  padding: 28px 24px;
  text-align: left;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--slate-200);
  transition: all 0.4s var(--ease);
}
.testimonial-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}
.testimonial-header {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 16px;
}
.testimonial-avatar {
  width: 48px;
  height: 48px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--brand-100), var(--brand-200));
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  font-weight: 700;
  color: var(--brand-700);
  flex-shrink: 0;
}
.testimonial-name { font-weight: 700; color: var(--text); font-size: 15px; }
.testimonial-role { font-size: 12px; color: var(--text-muted); }
.testimonial-text {
  font-size: 14px;
  color: var(--text-secondary);
  line-height: 1.7;
  font-style: italic;
  position: relative;
  padding-left: 16px;
  border-left: 3px solid var(--brand-200);
}
.testimonial-stars {
  margin-top: 12px;
  color: var(--brand-500);
  font-size: 14px;
  letter-spacing: 2px;
}

/* === RESPONSIVE === */
@media (max-width: 1024px) {
  .courses-grid, .news-grid { grid-template-columns: repeat(2, 1fr); }
  .why-grid { grid-template-columns: repeat(2, 1fr); }
  .footer-grid { grid-template-columns: repeat(2, 1fr); }
  .about-grid { gap: 32px; }
}

@media (max-width: 768px) {
  :root { --section-py: 64px; }

  .top-bar { display: none; }

  .header { padding: 12px 0; }
  .logo img { width: 40px; height: 40px; }
  .logo-text h1 { font-size: 18px; }

  .nav .container { justify-content: flex-end; }
  .nav-toggle { display: block; }
  .nav-list {
    display: none;
    flex-direction: column;
    width: 100%;
    position: absolute;
    top: 100%;
    left: 0;
    background: var(--slate-800);
    border-top: 1px solid rgba(255,255,255,0.06);
  }
  .nav-list.active { display: flex; }
  .nav-list a { padding: 14px 24px; border-bottom: 1px solid rgba(255,255,255,0.04); }

  .hero { height: 440px; }
  .hero-content { padding: 0 24px; }
  .hero-content h2 { font-size: 28px; }
  .hero-content p { font-size: 15px; }
  .hero-buttons { flex-direction: column; }
  .btn { width: 100%; text-align: center; }

  .stats-grid { grid-template-columns: repeat(2, 1fr); }
  .stat-item:not(:last-child)::after { display: none; }

  .about-grid { grid-template-columns: 1fr; }
  .about-features { grid-template-columns: 1fr; }

  .courses-grid, .news-grid, .why-grid { grid-template-columns: 1fr; }
  .footer-grid { grid-template-columns: 1fr; gap: 32px; }

  .section-header h2 { font-size: 28px; }
  .cta h2 { font-size: 26px; }

  .back-to-top { bottom: 20px; right: 20px; width: 42px; height: 42px; }
}