/* netopedia landing page. No external fonts or scripts: works offline in the classroom. */
:root {
  --bg: #f3f7fa; --surface: #ffffff; --ink: #0d1b2a; --sub: #4a5b6c; --line: #dbe4ec;
  --brand: #0291bd; --brand2: #00a8e4; --shadow: 0 1px 2px rgb(13 27 42 / .06), 0 8px 24px rgb(13 27 42 / .06);
  /* one colour per OSI layer (7 → 1) */
  --l7: #8b5cf6; --l6: #c026d3; --l5: #e11d48; --l4: #f59e0b; --l3: #10b981; --l2: #0ea5e9; --l1: #475569;
  --mono: ui-monospace, "Cascadia Code", "SF Mono", Consolas, "Liberation Mono", monospace;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0a1622; --surface: #102131; --ink: #e6eef5; --sub: #9db0c2; --line: #1f3447;
    --shadow: 0 1px 2px rgb(0 0 0 / .3), 0 10px 30px rgb(0 0 0 / .25); color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #0a1622; --surface: #102131; --ink: #e6eef5; --sub: #9db0c2; --line: #1f3447;
  --shadow: 0 1px 2px rgb(0 0 0 / .3), 0 10px 30px rgb(0 0 0 / .25); color-scheme: dark;
}

* { box-sizing: border-box; }
html, body { margin: 0; }
body {
  min-height: 100vh; display: flex; flex-direction: column;
  background: var(--bg); color: var(--ink); font: 16px/1.55 var(--sans);
  -webkit-font-smoothing: antialiased;
}

/* ---------- header ---------- */
.site-header {
  position: relative; display: grid; grid-template-columns: 1fr auto 1fr; align-items: center; gap: 24px;
  padding: 18px clamp(16px, 4vw, 48px); background: var(--surface); border-bottom: 1px solid var(--line);
}
.header-left { justify-self: start; }
.header-right { justify-self: end; margin-right: 44px; }
.logo { display: block; height: 64px; width: auto; }
/* logos are made for a light background: give them a white plate in dark mode */
:root[data-theme="dark"] .logo { background: #fff; border-radius: 10px; padding: 6px 8px; }
@media (prefers-color-scheme: dark) { :root:not([data-theme="light"]) .logo { background: #fff; border-radius: 10px; padding: 6px 8px; } }
.wordmark { text-align: center; }
.wordmark h1 {
  margin: 0; font: 800 clamp(2rem, 4.5vw, 3rem)/1 var(--sans); letter-spacing: -.03em;
}
.wordmark h1 span { color: var(--brand2); }
.wordmark p { margin: 6px 0 0; color: var(--sub); font-size: .95rem; }
.theme-btn {
  position: absolute; top: 50%; right: clamp(8px, 1.5vw, 16px); transform: translateY(-50%);
  width: 36px; height: 36px; border-radius: 50%; border: 1px solid var(--line);
  background: var(--bg); color: var(--ink); font-size: 18px; cursor: pointer;
}
.theme-btn:hover { border-color: var(--brand2); }

/* ---------- layer ribbon ---------- */
.stack { display: grid; grid-template-columns: repeat(7, 1fr); }
.stack span {
  padding: 5px 4px; text-align: center; color: #fff; font: 600 .72rem/1.2 var(--mono);
  letter-spacing: .02em; white-space: nowrap; overflow: hidden; text-overflow: ellipsis;
}
.stack .l7 { background: var(--l7); } .stack .l6 { background: var(--l6); } .stack .l5 { background: var(--l5); }
.stack .l4 { background: var(--l4); } .stack .l3 { background: var(--l3); } .stack .l2 { background: var(--l2); }
.stack .l1 { background: var(--l1); }

/* ---------- intro ---------- */
main { flex: 1; width: 100%; max-width: 1180px; margin: 0 auto; padding: clamp(24px, 4vw, 48px) clamp(16px, 4vw, 32px); }
.intro { margin-bottom: 28px; }
.intro h2 { margin: 18px 0 6px; font-size: 1.6rem; letter-spacing: -.01em; }
.lead { margin: 0; max-width: 70ch; color: var(--sub); }
.frame { display: inline-flex; margin: 0; border-radius: 8px; overflow: hidden; box-shadow: var(--shadow); font: 600 .78rem/1 var(--mono); }
.frame b { padding: 8px 12px; color: #fff; font-weight: 600; }
.h-eth { background: var(--l2); } .h-ip { background: var(--l3); } .h-tcp { background: var(--l4); }
.h-data { background: var(--l7); padding-inline: 22px !important; } .h-fcs { background: var(--l1); }

/* ---------- tool cards ---------- */
.tools { display: grid; grid-template-columns: repeat(auto-fit, minmax(min(100%, 460px), 1fr)); gap: 20px; }
.card {
  display: flex; flex-direction: column; color: inherit; text-decoration: none;
  background: var(--surface); border: 1px solid var(--line); border-radius: 14px; overflow: hidden;
  box-shadow: var(--shadow); transition: transform .15s ease, border-color .15s ease, box-shadow .15s ease;
}
.card:hover, .card:focus-visible { transform: translateY(-3px); border-color: var(--brand2); outline: none; box-shadow: 0 0 0 3px rgb(0 168 228 / .18), var(--shadow); }
.card-head {
  display: flex; align-items: center; gap: 12px; padding: 10px 16px;
  border-bottom: 1px dashed var(--line); font: .78rem/1 var(--mono); color: var(--sub);
}
.step { font-weight: 700; color: var(--brand); }
.layers { display: inline-flex; flex-direction: row-reverse; gap: 3px; } /* L7 left … L1 right, like the ribbon */
.layers i { width: 14px; height: 8px; border-radius: 2px; background: var(--line); }
.layers i.on:nth-child(1) { background: var(--l1); } .layers i.on:nth-child(2) { background: var(--l2); }
.layers i.on:nth-child(3) { background: var(--l3); } .layers i.on:nth-child(4) { background: var(--l4); }
.layers i.on:nth-child(5) { background: var(--l5); } .layers i.on:nth-child(6) { background: var(--l6); }
.layers i.on:nth-child(7) { background: var(--l7); }
.tag { margin-left: auto; padding: 3px 8px; border: 1px solid var(--line); border-radius: 999px; }
.card-body { flex: 1; display: flex; gap: 18px; padding: 20px 20px 16px; }
.icon { flex: none; width: 56px; height: 56px; padding: 8px; border-radius: 12px; background: var(--bg); border: 1px solid var(--line); }
.card h3 { margin: 2px 0 6px; font-size: 1.2rem; }
.card p { margin: 0; color: var(--sub); font-size: .95rem; }
.card-foot {
  display: flex; align-items: center; justify-content: space-between; padding: 10px 20px;
  background: color-mix(in srgb, var(--bg) 60%, var(--surface)); border-top: 1px solid var(--line);
}
.card-foot code { font: .8rem var(--mono); color: var(--sub); }
.go { font-weight: 600; color: var(--brand2); }
.card:hover .go { text-decoration: underline; }

/* ---------- footer ---------- */
.site-footer {
  display: flex; flex-wrap: wrap; justify-content: space-between; gap: 8px 24px;
  padding: 16px clamp(16px, 4vw, 48px); border-top: 1px solid var(--line); background: var(--surface);
  color: var(--sub); font-size: .85rem;
}
.ver { font-family: var(--mono); }

/* ---------- small screens ---------- */
@media (max-width: 720px) {
  .site-header { grid-template-columns: auto 1fr auto; gap: 12px; padding-right: 56px; }
  .header-right { margin-right: 0; }
  .logo { height: 40px; }
  .wordmark p { display: none; }
  .stack { grid-template-columns: repeat(7, 1fr); }
  .stack span { font-size: 0; padding: 4px 0; }
  .stack span::first-letter { font-size: .72rem; }
  .card-body { flex-direction: column; gap: 12px; }
}
@media (prefers-reduced-motion: reduce) { .card { transition: none; } .card:hover { transform: none; } }