:root {
  --bg: #f7f6f2;
  --surface: #ffffff;
  --text: #1d1f24;
  --muted: #5d6270;
  --line: #e3e1da;
  --accent: #1f6feb;
  --accent-soft: #e8f0fe;
  --note-bg: #fff8e6;
  --note-line: #f0d48a;
  --radius: 14px;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #111317;
    --surface: #181b21;
    --text: #e7e9ee;
    --muted: #9aa1b0;
    --line: #2a2f38;
    --accent: #6ea8ff;
    --accent-soft: #1b2638;
    --note-bg: #2a2413;
    --note-line: #5c4a1c;
    color-scheme: dark;
  }
}

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 16px/1.7 "Inter", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
}
a { color: var(--accent); text-underline-offset: 2px; }
a:hover { text-decoration-thickness: 2px; }

[data-lang="en"] .vi, [data-lang="vi"] .en { display: none !important; }
html:not([data-lang]) .vi { display: none !important; }

.topbar {
  position: sticky; top: 0; z-index: 10;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--line);
}
.topbar-inner {
  max-width: 820px; margin: 0 auto; padding: 12px 16px;
  display: flex; align-items: center; justify-content: space-between; gap: 12px;
}
.brand { display: flex; align-items: center; gap: 10px; color: var(--text); text-decoration: none; font-weight: 700; }
.brand img { width: 32px; height: 32px; border-radius: 8px; }
.nav { display: flex; align-items: center; gap: 4px; flex-wrap: wrap; justify-content: flex-end; }
.nav a { color: var(--muted); text-decoration: none; padding: 6px 10px; border-radius: 8px; font-size: 14px; }
.nav a:hover, .nav a[aria-current="page"] { color: var(--text); background: var(--accent-soft); }
.lang-switch { display: inline-flex; border: 1px solid var(--line); border-radius: 999px; padding: 2px; margin-left: 6px; }
.lang-switch button {
  border: 0; background: transparent; color: var(--muted); font: inherit; font-size: 13px; font-weight: 600;
  padding: 3px 10px; border-radius: 999px; cursor: pointer;
}
.lang-switch button[aria-pressed="true"] { background: var(--accent); color: #fff; }

main { max-width: 820px; margin: 0 auto; padding: 40px 16px 64px; }
.doc {
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  padding: clamp(22px, 5vw, 48px);
}
h1 { font-size: clamp(28px, 5vw, 38px); line-height: 1.2; margin: 0 0 8px; letter-spacing: -0.02em; }
h2 { font-size: 21px; line-height: 1.35; margin: 40px 0 10px; padding-top: 8px; letter-spacing: -0.01em; }
h3 { font-size: 17px; margin: 24px 0 6px; }
p, ul, ol { margin: 0 0 14px; }
ul, ol { padding-left: 22px; }
li { margin: 4px 0; }
.meta { color: var(--muted); font-size: 14px; margin-bottom: 24px; }
.summary {
  background: var(--accent-soft); border-radius: 10px; padding: 16px 20px; margin: 20px 0 8px;
}
.summary ul { margin: 0; }
.note {
  background: var(--note-bg); border: 1px solid var(--note-line); border-radius: 10px; padding: 14px 18px; margin: 16px 0;
}
.toc { border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); padding: 14px 0; margin: 24px 0 8px; font-size: 15px; }
.toc ol { margin: 0; columns: 2; column-gap: 32px; }
@media (max-width: 600px) { .toc ol { columns: 1; } }
table { width: 100%; border-collapse: collapse; margin: 8px 0 16px; font-size: 15px; }
th, td { text-align: left; vertical-align: top; padding: 9px 10px; border-bottom: 1px solid var(--line); }
th { color: var(--muted); font-weight: 600; font-size: 13px; text-transform: uppercase; letter-spacing: .04em; }
.table-wrap { overflow-x: auto; }
code { font-family: ui-monospace, "Cascadia Code", Consolas, monospace; font-size: .9em; background: var(--accent-soft); padding: 1px 5px; border-radius: 5px; }

.hero { text-align: center; padding: 24px 0 8px; }
.hero img { width: 96px; height: 96px; border-radius: 22px; }
.hero p { color: var(--muted); max-width: 560px; margin: 8px auto 0; }
.cards { display: grid; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); gap: 16px; margin-top: 32px; }
.card {
  display: block; background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 22px; text-decoration: none; color: var(--text); transition: border-color .15s, transform .15s;
}
.card:hover { border-color: var(--accent); transform: translateY(-2px); }
.card strong { display: block; font-size: 18px; margin-bottom: 4px; }
.card span { color: var(--muted); font-size: 15px; }

footer { max-width: 820px; margin: 0 auto; padding: 0 16px 40px; color: var(--muted); font-size: 14px; display: flex; gap: 16px; flex-wrap: wrap; justify-content: space-between; }
footer a { color: var(--muted); }