:root {
  --bg0: #070b1d;
  --bg1: #111a3b;
  --surface: rgba(14, 21, 46, 0.82);
  --surface2: rgba(26, 34, 70, 0.78);
  --text: #f4f7ff;
  --muted: #b7c4e0;
  --border: rgba(173, 194, 235, 0.28);
  --accent: #61dafb;
  --accent2: #9f7aea;
  --warn: #f6c453;
  --danger: #ff6b6b;
}

* { box-sizing: border-box; }

html, body { margin: 0; padding: 0; }

body {
  font-family: system-ui, -apple-system, "Segoe UI", "Noto Sans Thai", "Noto Sans", Arial, sans-serif;
  line-height: 1.65;
  color: var(--text);
  background: linear-gradient(160deg, var(--bg0), var(--bg1));
  min-height: 100vh;
  position: relative;
}


a,
a:visited {
  color: var(--accent);
  text-decoration-color: rgba(97, 218, 251, 0.55);
}

a:hover,
a:focus-visible,
a:active {
  color: #b9f0ff;
  text-decoration: underline;
  text-underline-offset: 2px;
}

a:focus-visible {
  outline: 2px solid rgba(97, 218, 251, 0.65);
  outline-offset: 2px;
  border-radius: 0.25rem;
}

body::before {
  content: "";
  position: fixed;
  inset: 0;
  background-image:
    radial-gradient(2px 2px at 12% 14%, rgba(255,255,255,0.55), transparent 60%),
    radial-gradient(1px 1px at 24% 80%, rgba(255,255,255,0.45), transparent 60%),
    radial-gradient(1.5px 1.5px at 66% 22%, rgba(255,255,255,0.45), transparent 60%),
    radial-gradient(2px 2px at 88% 72%, rgba(255,255,255,0.45), transparent 60%),
    radial-gradient(1px 1px at 42% 46%, rgba(255,255,255,0.4), transparent 60%);
  pointer-events: none;
  z-index: -2;
}

body::after {
  content: "";
  position: fixed;
  inset: -20% -10%;
  background:
    radial-gradient(circle at 20% 20%, rgba(97, 218, 251, 0.1), transparent 35%),
    radial-gradient(circle at 80% 30%, rgba(159, 122, 234, 0.14), transparent 38%);
  pointer-events: none;
  z-index: -1;
}

.container { width: min(1040px, 92%); margin: 0 auto; }

.topbar {
  border-bottom: 1px solid var(--border);
  background: rgba(7, 11, 29, 0.78);
  backdrop-filter: blur(8px);
  position: sticky;
  top: 0;
  z-index: 30;
}

.nav-wrap { display: flex; align-items: center; justify-content: space-between; padding: 0.75rem 0; gap: 1rem; }
.brand { text-decoration: none; color: var(--text); }
.brand:visited { color: var(--text); text-decoration: none; }
.brand strong { display: block; font-size: 1.1rem; letter-spacing: 0.4px; }
.brand span { color: var(--muted); font-size: 0.8rem; }

.nav-toggle { display: none; }
.nav-toggle-label { display: none; color: var(--text); border: 1px solid var(--border); padding: 0.25rem 0.55rem; border-radius: 0.5rem; }
.nav-links { display: flex; flex-wrap: wrap; gap: 0.45rem; }
.nav-links a {
  text-decoration: none;
  color: var(--text);
}
.nav-links a:visited {
  color: var(--text);
  text-decoration: none;
}
.nav-links a {
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 0.3rem 0.7rem;
  font-size: 0.92rem;
}
.nav-links a:hover, .nav-links a.active { border-color: var(--accent); background: rgba(97, 218, 251, 0.16); }

.hero {
  padding: 2.6rem 0 1.8rem;
}
.hero-card, .card, .section-box, .callout {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 1rem;
}
.hero-card { padding: 1.4rem; box-shadow: 0 14px 36px rgba(0,0,0,0.24); }
.hero h1 { margin: 0 0 0.45rem; font-size: clamp(1.5rem, 2.5vw, 2.2rem); }
.hero p { margin: 0; color: var(--muted); }

.sf-logo {
  display: block;
  margin: 1rem auto 1rem;
  width: min(420px, 70vw);
  max-width: 420px;
  height: auto;
}

.cta-row { margin-top: 1rem; display: flex; flex-wrap: wrap; gap: 0.6rem; }
.btn {
  display: inline-block;
  text-decoration: none;
  border-radius: 0.7rem;
  padding: 0.52rem 0.95rem;
  border: 1px solid var(--border);
  color: var(--text);
}
.btn:visited {
  color: var(--text);
  text-decoration: none;
}
.btn.primary { background: linear-gradient(120deg, rgba(97,218,251,0.24), rgba(159,122,234,0.26)); border-color: rgba(97,218,251,0.45); }
.btn.ghost:hover, .btn.primary:hover { transform: translateY(-1px); }

.grid {
  display: grid;
  grid-template-columns: repeat(12, 1fr);
  gap: 0.9rem;
}
.card { padding: 1rem; }
.sf-card {
  margin: 0.8rem 0 1rem;
  background: var(--surface2);
}
.card h3 { margin-top: 0; }
.card p { color: var(--muted); }
.card-3 { grid-column: span 6; }
.tag { display: inline-block; font-size: 0.74rem; border: 1px solid var(--border); color: var(--muted); border-radius: 999px; padding: 0.1rem 0.45rem; margin-right: 0.3rem; }

.section-box { padding: 1rem 1.1rem; margin-top: 1rem; }
.section-box h2 { margin-top: 0; }

.callout { margin: 1rem 0; padding: 0.85rem 0.95rem; background: var(--surface2); }
.callout .label { font-size: 0.82rem; letter-spacing: 0.2px; font-weight: 700; margin-bottom: 0.3rem; }
.callout.note { border-left: 4px solid var(--accent); }
.callout.tip { border-left: 4px solid var(--accent); }
.callout.caution { border-left: 4px solid var(--warn); }
.callout.teacher { border-left: 4px solid var(--accent2); }

.mono {
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
  font-size: 0.95em;
}

.breadcrumb { font-size: 0.9rem; color: var(--muted); margin: 1rem 0 0.5rem; }
.breadcrumb a { color: var(--accent); text-decoration: none; }
.breadcrumb a:visited { color: var(--accent); text-decoration: none; }
.breadcrumb a:hover, .breadcrumb a:focus-visible, .breadcrumb a:active { text-decoration: underline; }

.steps { counter-reset: s; list-style: none; padding: 0; margin: 0; }
.steps li {
  counter-increment: s;
  margin: 0.5rem 0;
  padding: 0.65rem 0.8rem 0.65rem 2.2rem;
  background: rgba(255,255,255,0.03);
  border: 1px solid var(--border);
  border-radius: 0.8rem;
  position: relative;
}
.steps li::before {
  content: counter(s);
  position: absolute;
  left: 0.7rem;
  top: 0.62rem;
  width: 1.2rem;
  height: 1.2rem;
  border-radius: 50%;
  background: rgba(97,218,251,0.22);
  border: 1px solid rgba(97,218,251,0.6);
  display: grid;
  place-items: center;
  font-size: 0.78rem;
  font-weight: 700;
}

.figure { margin: 1rem 0; }
.sf-figure {
  border: 1px solid var(--border);
  border-radius: 0.8rem;
  background: var(--surface2);
  padding: 0.8rem;
}
.sf-figure img {
  width: 100%;
  max-width: 100%;
  height: auto;
  display: block;
  border-radius: 0.55rem;
  border: 1px solid var(--border);
}
.img-placeholder {
  aspect-ratio: 16 / 9;
  border-radius: 0.8rem;
  border: 1px dashed rgba(255,255,255,0.4);
  background:
    linear-gradient(rgba(255,255,255,0.03), rgba(255,255,255,0.03)),
    repeating-linear-gradient(0deg, transparent, transparent 23px, rgba(255,255,255,0.05) 24px),
    repeating-linear-gradient(90deg, transparent, transparent 23px, rgba(255,255,255,0.05) 24px);
  display: grid;
  place-items: center;
  text-align: center;
  padding: 1rem;
}
.img-placeholder__title { font-weight: 800; letter-spacing: 1px; color: var(--accent); }
.img-placeholder__desc { color: var(--muted); font-size: 0.95rem; }
figcaption { color: var(--muted); font-size: 0.9rem; margin-top: 0.4rem; }

.bottom-nav { display: flex; justify-content: space-between; gap: 0.7rem; margin-top: 1.2rem; flex-wrap: wrap; }

footer {
  margin-top: 2rem;
  border-top: 1px solid var(--border);
  padding: 1.3rem 0 2rem;
  color: var(--muted);
  font-size: 0.92rem;
}

@media (max-width: 860px) {
  .card-3 { grid-column: span 12; }
  .nav-toggle-label { display: inline-block; }
  .nav-links {
    display: none;
    position: absolute;
    right: 4%;
    top: 62px;
    width: min(92vw, 360px);
    background: rgba(7, 11, 29, 0.96);
    border: 1px solid var(--border);
    border-radius: 0.8rem;
    padding: 0.7rem;
    flex-direction: column;
  }
  .nav-toggle:checked ~ .nav-links { display: flex; }
}

@media print {
  body { background: #fff !important; color: #000 !important; }
  body::before, body::after, .topbar { display: none !important; }
  .hero-card, .card, .section-box, .callout { border: 1px solid #bbb !important; background: #fff !important; color: #000 !important; box-shadow: none !important; }
  .btn { display: none !important; }
  a { color: #000 !important; text-decoration: underline; }
  figcaption, .img-placeholder__desc, .card p { color: #222 !important; }
}