:root {
  --bg: #070b1a;
  --bg-2: #0d1430;
  --card: #111a3a;
  --border: #1f2b57;
  --text: #dbe3ff;
  --muted: #8f9bc7;
  --accent: #4fd1ff;
  --accent-2: #ffb547;
  --danger: #ff6b6b;
  --radius: 14px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  line-height: 1.65;
  color: var(--text);
  background:
    radial-gradient(ellipse at 20% -10%, #1b2a6b 0%, transparent 55%),
    radial-gradient(ellipse at 90% 10%, #3a1650 0%, transparent 45%),
    var(--bg);
  background-attachment: fixed;
  min-height: 100vh;
}

/* tiny starfield */
body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  background-image:
    radial-gradient(1px 1px at 10% 20%, #fff8 50%, transparent 51%),
    radial-gradient(1px 1px at 30% 70%, #fff6 50%, transparent 51%),
    radial-gradient(1.5px 1.5px at 55% 35%, #fff9 50%, transparent 51%),
    radial-gradient(1px 1px at 75% 80%, #fff5 50%, transparent 51%),
    radial-gradient(1px 1px at 85% 15%, #fff7 50%, transparent 51%),
    radial-gradient(1.5px 1.5px at 45% 90%, #fff6 50%, transparent 51%),
    radial-gradient(1px 1px at 65% 55%, #fff5 50%, transparent 51%);
  z-index: -1;
}

a { color: var(--accent); }
a:hover { color: #9be6ff; }

/* ---------- header ---------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  background: rgba(7, 11, 26, 0.85);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
}

.nav {
  max-width: 960px;
  margin: 0 auto;
  padding: 12px 16px;
  display: flex;
  align-items: center;
  gap: 16px;
  flex-wrap: wrap;
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 700;
  letter-spacing: 0.5px;
  color: var(--text);
  text-decoration: none;
  margin-right: auto;
}

.brand-logo {
  width: 32px;
  height: 32px;
}

.nav-links {
  display: flex;
  gap: 4px;
  flex-wrap: wrap;
}

.nav-links a {
  color: var(--muted);
  text-decoration: none;
  padding: 6px 10px;
  border-radius: 8px;
  font-size: 0.95rem;
}

.nav-links a:hover { color: var(--text); background: var(--bg-2); }
.nav-links a.active { color: var(--text); background: var(--card); }

.lang-switch {
  display: flex;
  border: 1px solid var(--border);
  border-radius: 999px;
  overflow: hidden;
}

.lang-switch button {
  background: transparent;
  color: var(--muted);
  border: 0;
  padding: 5px 12px;
  font: inherit;
  font-size: 0.85rem;
  cursor: pointer;
}

.lang-switch button.active {
  background: var(--accent);
  color: #04122a;
  font-weight: 700;
}

/* ---------- language blocks ---------- */
html[lang="en"] [data-lang="vi"],
html[lang="vi"] [data-lang="en"] { display: none !important; }

/* ---------- content ---------- */
main {
  max-width: 860px;
  margin: 0 auto;
  padding: 32px 16px 64px;
}

.hero {
  text-align: center;
  padding: 40px 0 24px;
}

.hero h1 {
  font-size: clamp(2rem, 6vw, 3.2rem);
  margin: 8px 0;
  letter-spacing: 1px;
  background: linear-gradient(90deg, var(--accent), #a78bfa, var(--accent-2));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

.hero p { color: var(--muted); max-width: 600px; margin: 0 auto; }

.hero-logo { width: 96px; height: 96px; }

.badges {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 8px;
  margin: 20px 0 0;
  padding: 0;
  list-style: none;
}

.badges li {
  background: var(--card);
  border: 1px solid var(--border);
  padding: 4px 12px;
  border-radius: 999px;
  font-size: 0.85rem;
  color: var(--text);
}

.cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 16px;
  margin-top: 32px;
}

.card {
  display: block;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  text-decoration: none;
  color: var(--text);
  transition: transform 0.15s, border-color 0.15s;
}

.card:hover { transform: translateY(-3px); border-color: var(--accent); color: var(--text); }
.card h2 { margin: 0 0 6px; font-size: 1.15rem; }
.card p { margin: 0; color: var(--muted); font-size: 0.95rem; }
.card .icon { font-size: 1.6rem; }

.doc h1 { font-size: clamp(1.7rem, 5vw, 2.3rem); margin-bottom: 4px; }

.meta { color: var(--muted); font-size: 0.9rem; margin-top: 0; }

.doc h2 {
  margin-top: 40px;
  padding-top: 8px;
  font-size: 1.3rem;
  color: var(--accent);
  border-top: 1px solid var(--border);
}

.doc h3 { margin-top: 24px; font-size: 1.05rem; }

.toc {
  background: var(--bg-2);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px 20px;
  margin: 24px 0;
}

.toc strong { display: block; margin-bottom: 6px; }
.toc ol { margin: 0; padding-left: 20px; }
.toc a { text-decoration: none; }

.note {
  background: rgba(79, 209, 255, 0.08);
  border-left: 4px solid var(--accent);
  padding: 12px 16px;
  border-radius: 8px;
  margin: 16px 0;
}

.note.warn {
  background: rgba(255, 107, 107, 0.08);
  border-left-color: var(--danger);
}

.table-wrap { overflow-x: auto; margin: 16px 0; }

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.95rem;
  min-width: 520px;
}

th, td {
  text-align: left;
  vertical-align: top;
  padding: 10px 12px;
  border-bottom: 1px solid var(--border);
}

th { background: var(--bg-2); color: var(--accent-2); font-weight: 600; }

.steps { counter-reset: step; list-style: none; padding: 0; }

.steps li {
  counter-increment: step;
  position: relative;
  padding: 12px 12px 12px 52px;
  margin-bottom: 10px;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
}

.steps li::before {
  content: counter(step);
  position: absolute;
  left: 14px;
  top: 12px;
  width: 26px;
  height: 26px;
  border-radius: 50%;
  background: var(--accent);
  color: #04122a;
  font-weight: 700;
  text-align: center;
  line-height: 26px;
  font-size: 0.85rem;
}

code {
  background: var(--bg-2);
  border: 1px solid var(--border);
  padding: 1px 6px;
  border-radius: 6px;
  font-size: 0.9em;
}

/* ---------- footer ---------- */
.site-footer {
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: 0.85rem;
  text-align: center;
  padding: 24px 16px;
}

.site-footer a { color: var(--muted); }

@media (max-width: 600px) {
  .nav { gap: 10px; }
  .brand { width: 100%; }
}