/* ============================================================
   Vietnam School of Science — Bright Blue & White Theme
   ============================================================ */

:root {
  --bg-primary: #ffffff;
  --bg-secondary: #f0f4f8;
  --bg-card: #f7f9fc;
  --bg-card-hover: #edf2f7;
  --bg-elevated: #ffffff;
  --text-primary: #0f1d35;
  --text-secondary: #3d5271;
  --text-muted: #8096b0;
  --accent: #1a56db;
  --accent-hover: #1545b5;
  --accent-light: #dbeafe;
  --accent-lighter: #eff6ff;
  --blue-dark: #0f2b5b;
  --blue-mid: #2563eb;
  --blue-light: #60a5fa;
  --border: rgba(15, 45, 90, 0.1);
  --border-strong: rgba(15, 45, 90, 0.2);
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --radius-xl: 28px;
  --shadow: 0 8px 30px rgba(15, 45, 90, 0.08);
  --max-w: 1200px;
  --gutter: clamp(1rem, 4vw, 2.5rem);
}

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

html { scroll-behavior: smooth; }

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

a { color: inherit; text-decoration: none; }
img { max-width: 100%; display: block; }
ul, ol { list-style: none; }

.skip-link {
  position: absolute; left: -9999px; top: auto;
}
.skip-link:focus {
  left: 1rem; top: 1rem; z-index: 9999;
  background: var(--accent); color: #fff;
  padding: 0.6rem 1rem; border-radius: var(--radius-sm); font-weight: 600;
}

/* ─── Buttons ─────────────────────────────────── */
.btn {
  display: inline-flex; align-items: center; justify-content: center;
  padding: 0.65rem 1.5rem; border-radius: 999px; font-weight: 600;
  font-size: 0.9rem; transition: all 0.2s ease; border: none; cursor: pointer;
  text-decoration: none; gap: 0.5rem; font-family: inherit;
}
.btn--accent {
  background: var(--accent); color: #ffffff;
}
.btn--accent:hover { background: var(--accent-hover); transform: translateY(-1px); }
.btn--outline {
  background: transparent; border: 1.5px solid var(--accent);
  color: var(--accent);
}
.btn--outline:hover { border-color: var(--accent-hover); background: var(--accent-lighter); }
.btn--lg { padding: 0.85rem 2rem; font-size: 1rem; }
.btn--sm { padding: 0.45rem 1rem; font-size: 0.82rem; }

/* ─── Header ──────────────────────────────────── */
.site-header {
  position: fixed; top: 0; left: 0; right: 0; z-index: 200;
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(20px); -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border);
  box-shadow: 0 1px 3px rgba(15, 45, 90, 0.06);
}
.header-inner {
  max-width: var(--max-w); margin: 0 auto;
  display: flex; align-items: center; gap: 1.5rem;
  padding: 0.75rem var(--gutter);
}

.logo {
  display: flex; align-items: center; gap: 0.55rem;
  text-decoration: none; color: var(--text-primary); flex-shrink: 0;
}
.logo-img {
  height: 40px; width: auto; display: block;
}
.logo-text { font-weight: 800; font-size: 1.2rem; letter-spacing: -0.02em; color: var(--blue-dark); }

.header-cta { margin-left: auto; }
.header-cta.btn--accent { background: var(--accent); color: #fff; }

.menu-trigger {
  display: flex; align-items: center; justify-content: center;
  width: 40px; height: 40px; background: none; border: 1px solid var(--border);
  border-radius: var(--radius-sm); cursor: pointer; position: relative;
  color: var(--blue-dark);
}
.hamburger, .hamburger::before, .hamburger::after {
  display: block; width: 18px; height: 2px;
  background: var(--blue-dark); border-radius: 2px;
  transition: transform 0.25s ease;
}
.hamburger { position: relative; }
.hamburger::before, .hamburger::after {
  content: ''; position: absolute; left: 0;
}
.hamburger::before { top: -6px; }
.hamburger::after { top: 6px; }
.menu-trigger[aria-expanded="true"] .hamburger { background: transparent; }
.menu-trigger[aria-expanded="true"] .hamburger::before { top: 0; transform: rotate(45deg); }
.menu-trigger[aria-expanded="true"] .hamburger::after { top: 0; transform: rotate(-45deg); }

/* ─── Navigation ──────────────────────────────── */
.main-nav {
  display: none; position: fixed; top: 60px; left: 0; right: 0; bottom: 0;
  background: #ffffff; padding: 1rem var(--gutter) 2rem;
  overflow-y: auto; z-index: 199;
}
.main-nav.open { display: block; }

.nav-tree { display: grid; gap: 0.15rem; }
.submenu { display: none; padding-left: 1rem; border-left: 2px solid var(--border); margin-top: 0.15rem; }
.nav-item.expanded > .submenu { display: block; }

.menu-row {
  display: flex; align-items: center; gap: 0.4rem; position: relative;
}
.menu-link {
  display: block; width: 100%; padding: 0.6rem 0.7rem;
  color: var(--text-secondary); border-radius: var(--radius-sm);
  transition: all 0.15s ease; font-size: 0.95rem; font-weight: 500;
}
.menu-link:hover, .menu-link:focus-visible, .menu-link.active {
  color: var(--accent); background: var(--accent-lighter);
}
.menu-link.active { color: var(--accent); font-weight: 600; }

.submenu-toggle {
  width: 32px; height: 32px; flex-shrink: 0;
  border-radius: var(--radius-sm); border: 1px solid var(--border);
  background: transparent; color: var(--text-secondary);
  display: inline-flex; align-items: center; justify-content: center;
  cursor: pointer; transition: all 0.15s ease;
}
.submenu-toggle:hover { border-color: var(--accent); background: var(--accent-lighter); }
.submenu-toggle svg { width: 10px; height: 6px; transition: transform 0.2s ease; }
.nav-item.expanded > .menu-row > .submenu-toggle svg { transform: rotate(180deg); }

/* ─── Hero ────────────────────────────────────── */
.hero {
  min-height: 90vh; display: flex; flex-direction: column;
  justify-content: center; padding: 8rem var(--gutter) 3rem;
  position: relative; overflow: hidden;
  background:
    linear-gradient(135deg, #0f2b5b 0%, #1a56db 50%, #2563eb 100%);
  color: #ffffff;
}
.hero__inner { max-width: var(--max-w); margin: 0 auto; width: 100%; }
.hero__kicker {
  font-size: 0.82rem; font-weight: 700; letter-spacing: 0.18em;
  text-transform: uppercase; color: rgba(255,255,255,0.75); margin-bottom: 1.2rem;
}
.hero__title {
  font-size: clamp(2.8rem, 7vw, 5.5rem); font-weight: 900;
  line-height: 1.02; letter-spacing: -0.03em; margin-bottom: 1.5rem;
  color: #ffffff;
}
.hero__lead {
  font-size: clamp(1rem, 1.5vw, 1.25rem); color: rgba(255,255,255,0.85);
  max-width: 52ch; line-height: 1.7; margin-bottom: 2.5rem;
}
.hero__actions { display: flex; flex-wrap: wrap; gap: 0.85rem; margin-bottom: 4rem; }
.hero .btn--accent { background: #ffffff; color: var(--blue-dark); }
.hero .btn--accent:hover { background: #f0f4f8; }
.hero .btn--outline { border-color: rgba(255,255,255,0.4); color: #ffffff; }
.hero .btn--outline:hover { border-color: #ffffff; background: rgba(255,255,255,0.1); }

.hero__stats {
  display: grid; grid-template-columns: repeat(2, 1fr); gap: 1rem;
  max-width: var(--max-w); margin: 0 auto; width: 100%;
  padding-top: 2.5rem; border-top: 1px solid rgba(255,255,255,0.2);
}
.stat { display: flex; flex-direction: column; gap: 0.15rem; }
.stat__number { font-size: 1.5rem; font-weight: 800; letter-spacing: -0.02em; color: #ffffff; }
.stat__label { font-size: 0.82rem; color: rgba(255,255,255,0.6); text-transform: uppercase; letter-spacing: 0.05em; }

/* ─── Content shell ───────────────────────────── */
.content-shell {
  max-width: var(--max-w); margin: 0 auto;
  padding: 0 var(--gutter) 4rem;
}

/* ─── Content panel (SPA page container) ──────── */
.content-panel {
  border-radius: var(--radius-xl);
  border: 1px solid var(--border);
  background: #ffffff;
  overflow: hidden;
  box-shadow: var(--shadow);
}
.content-panel header {
  padding: clamp(1.5rem, 3vw, 2.5rem) clamp(1.2rem, 3vw, 2.2rem) 1rem;
}
.section-tag {
  font-size: 0.78rem; font-weight: 700; letter-spacing: 0.15em;
  text-transform: uppercase; color: var(--accent); margin-bottom: 0.5rem;
}
.content-panel h3 {
  font-size: clamp(1.4rem, 3vw, 2.2rem); font-weight: 800;
  line-height: 1.15; letter-spacing: -0.02em; margin-bottom: 0.6rem;
}
.content-panel .lead {
  color: var(--text-secondary); max-width: 60ch; font-size: 1.02rem;
}

/* ─── Card grid ───────────────────────────────── */
.card-grid {
  padding: 1rem clamp(1.2rem, 3vw, 2.2rem) clamp(1.5rem, 3vw, 2.2rem);
  display: grid; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 1rem;
}
.info-card {
  border-radius: var(--radius-md); border: 1px solid var(--border);
  padding: 1.2rem; background: var(--bg-secondary);
  transition: border-color 0.2s ease, transform 0.2s ease;
}
.info-card:hover { border-color: var(--accent); transform: translateY(-2px); box-shadow: 0 4px 12px rgba(26,86,219,0.1); }
.info-card h4 { font-size: 1rem; font-weight: 700; margin-bottom: 0.4rem; }
.info-card p { font-size: 0.92rem; color: var(--text-secondary); line-height: 1.55; }

/* ─── Photo card ───────────────────────────────── */
.photo-card {
  display: inline-block; max-width: 100%;
  background: var(--bg-secondary);
  border-radius: 1.25rem;
  overflow: hidden;
  box-shadow: 0 4px 24px rgba(15,43,91,0.10);
  border: 1px solid var(--border);
}
.photo-card img {
  display: block; max-width: 100%; height: auto;
}
.photo-card figcaption {
  padding: 0.75rem 1.1rem;
  font-size: 0.875rem; color: var(--text-secondary); line-height: 1.5;
}
.photo-card--full { display: block; width: 100%; }
.photo-card--full img { width: 100%; object-fit: cover; max-height: 480px; }

/* ─── Body wrap & quick links ─────────────────── */
.body-wrap {
  padding: 0.5rem clamp(1.2rem, 3vw, 2.2rem) clamp(1.5rem, 3vw, 2rem);
}
.body-wrap p { color: var(--text-secondary); max-width: 68ch; margin: 0.5rem 0; }

.quick-links {
  display: flex; flex-wrap: wrap; gap: 0.65rem; margin-top: 1.2rem;
}
.quick-links a {
  padding: 0.5rem 1rem; border-radius: 999px; font-size: 0.88rem;
  font-weight: 600; border: 1px solid var(--border);
  transition: all 0.2s ease; color: var(--accent);
}
.quick-links a:hover {
  border-color: var(--accent); color: #fff; background: var(--accent);
}

/* ─── Footer ──────────────────────────────────── */
.site-footer {
  border-top: 1px solid var(--border); margin-top: 2rem;
  color: var(--text-secondary); font-size: 0.88rem;
}
.footer__inner {
  max-width: var(--max-w); margin: 0 auto;
  padding: 3rem var(--gutter) 2rem;
}
.footer__brand {
  display: flex; align-items: center; gap: 0.5rem; flex-wrap: wrap;
  margin-bottom: 2rem;
}
.footer__tagline { width: 100%; color: var(--text-muted); font-size: 0.82rem; margin-top: 0.3rem; }
.footer__cols {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: 2rem; margin-bottom: 2.5rem;
}
.footer__col { display: flex; flex-direction: column; gap: 0.5rem; }
.footer__col h4 {
  font-size: 0.78rem; font-weight: 700; text-transform: uppercase;
  letter-spacing: 0.1em; color: var(--text-muted); margin-bottom: 0.3rem;
}
.footer__col a {
  color: var(--text-secondary); font-size: 0.88rem; transition: color 0.15s ease;
}
.footer__col a:hover { color: var(--accent); }

.footer__brand .logo-img { height: 32px; width: auto; }
.footer__bottom {
  border-top: 1px solid var(--border); padding-top: 1.5rem;
}
.footer__bottom p { color: var(--text-muted); font-size: 0.8rem; }

/* ─── Animations ──────────────────────────────── */
@keyframes fade-in { from { opacity: 0; transform: translateY(10px); } to { opacity: 1; transform: translateY(0); } }

/* ─── Desktop ─────────────────────────────────── */
@media (min-width: 980px) {
  .menu-trigger { display: none; }

  .main-nav {
    display: flex; position: static; background: none;
    padding: 0; overflow: visible;
  }

  .nav-tree {
    display: flex; gap: 0; align-items: center;
  }

  .nav-item { position: relative; }
  .nav-item > .menu-row > .menu-link {
    padding: 0.45rem 0.65rem; white-space: nowrap; font-size: 0.88rem;
  }

  .submenu {
    position: absolute; left: 50%; transform: translateX(-50%);
    top: calc(100% + 0.4rem);
    min-width: 220px; padding: 0.5rem;
    background: #ffffff; border: 1px solid var(--border);
    border-radius: var(--radius-md); box-shadow: var(--shadow);
  }

  /* Hover bridge */
  .nav-item.has-children > .menu-row::after {
    content: ''; position: absolute; bottom: -0.5rem;
    left: 0; right: 0; height: 0.5rem;
  }

  .submenu .submenu {
    left: calc(100% + 0.4rem); transform: none;
    top: -0.4rem;
  }

  .nav-item:hover > .submenu,
  .nav-item:focus-within > .submenu { display: block; }

  /* School archive 2-col */
  .nav-item[data-menu="school"] > .submenu {
    display: none;
    grid-template-columns: repeat(2, 1fr);
    min-width: 240px; column-gap: 0;
  }
  .nav-item[data-menu="school"]:hover > .submenu,
  .nav-item[data-menu="school"]:focus-within > .submenu { display: grid; }

  .submenu-toggle { display: none; }

  .hero__stats { grid-template-columns: repeat(4, 1fr); }
}