/* ============================================================
   Mastering — shared design system
   Direction: "engineering field notebook." The subject is
   schematics (packet flow, wire protocols, cluster topology), so
   the system leans on drafting conventions — ruled grid, spec-sheet
   labels, a trace/signal accent pair — instead of a generic
   SaaS-docs look. Every page on the site inherits from here.
   ============================================================ */

/* ---------- Self-hosted type ---------- */
@font-face {
  font-family: "IBM Plex Sans Condensed";
  src: url("../fonts/plex-sans-cond-600.woff2") format("woff2");
  font-weight: 600;
  font-style: normal;
  font-display: swap;
}
@font-face {
  font-family: "IBM Plex Sans Condensed";
  src: url("../fonts/plex-sans-cond-700.woff2") format("woff2");
  font-weight: 700;
  font-style: normal;
  font-display: swap;
}
@font-face {
  font-family: "Literata";
  src: url("../fonts/literata-400.woff2") format("woff2");
  font-weight: 400;
  font-style: normal;
  font-display: swap;
}
@font-face {
  font-family: "Literata";
  src: url("../fonts/literata-400i.woff2") format("woff2");
  font-weight: 400;
  font-style: italic;
  font-display: swap;
}
@font-face {
  font-family: "Literata";
  src: url("../fonts/literata-600.woff2") format("woff2");
  font-weight: 600;
  font-style: normal;
  font-display: swap;
}
@font-face {
  font-family: "IBM Plex Mono";
  src: url("../fonts/plex-mono-400.woff2") format("woff2");
  font-weight: 400;
  font-style: normal;
  font-display: swap;
}
@font-face {
  font-family: "IBM Plex Mono";
  src: url("../fonts/plex-mono-500.woff2") format("woff2");
  font-weight: 500;
  font-style: normal;
  font-display: swap;
}

/* ---------- Design tokens ---------- */
:root {
  /* Ink / paper */
  --ink: #14181f;
  --text: var(--ink);
  --text-muted: #5c6a68;
  --paper: #f2f5f4;
  --bg: var(--paper);
  --bg-elevated: #fdfefe;
  --border: #d7dfdd;
  --grid-line: rgba(20, 24, 31, 0.045);

  /* Trace (primary) / Signal (secondary) — two genuinely distinct
     accents already in use across the site: primary nav/links vs.
     "also relevant" cross-references. */
  --accent: #0a7c73;
  --accent-ink: #ffffff;
  --accent-2: #a55324;

  /* Status — its own lane, not counted as the accent. Chosen to
     match real protocol convention (SYN=go, FIN/RST=stop) that the
     interactive pages already lean on. */
  --ok: #146c43;
  --warn: #9a5b12;
  --danger: #b3261e;

  --code-bg: #e9eeec;
  --code-border: #d1dad8;

  /* Categorical swatches — for diagrams distinguishing several
     protocol layers/algorithms at once (OSI chip stack, TLS cipher
     suite anatomy), where two accents aren't enough. Two slots reuse
     --accent/--danger so the categorical set still reads as part of
     the same system rather than a bolted-on rainbow. */
  --swatch-violet: #6d28d9;
  --swatch-amber: #b45309;
  --swatch-indigo: #2543a8;
  --shadow: 0 1px 2px rgba(20, 24, 31, 0.05), 0 6px 20px rgba(20, 24, 31, 0.06);
  --radius: 6px;
  --radius-sm: 3px;

  /* Type roles */
  --font-display: "IBM Plex Sans Condensed", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --font-body: "Literata", Georgia, Cambria, "Times New Roman", Times, serif;
  --font-mono: "IBM Plex Mono", "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
}

/* ---------- Reset-ish base ---------- */
* { box-sizing: border-box; }

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

body {
  background-color: var(--bg);
  background-image:
    linear-gradient(var(--grid-line) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid-line) 1px, transparent 1px);
  background-size: 28px 28px;
  color: var(--text);
  font-family: var(--font-body);
  font-size: 1.05rem;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

code, pre, .mono { font-family: var(--font-mono); }

h1, h2, h3, h4 {
  font-family: var(--font-display);
  line-height: 1.2;
  font-weight: 700;
  text-wrap: balance;
}

p { max-width: 68ch; }

a {
  color: var(--accent);
  text-decoration: none;
}
a:hover { text-decoration: underline; }

a:focus-visible, button:focus-visible, input:focus-visible, .term:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
  border-radius: 2px;
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
    scroll-behavior: auto !important;
  }
}

/* ---------- Layout ---------- */
.container {
  max-width: 920px;
  margin: 0 auto;
  padding: 32px 24px 96px;
}

.page-header {
  margin-bottom: 32px;
}

.page-header h1 {
  font-size: 2.15rem;
  letter-spacing: -0.01em;
  margin: 0 0 8px;
}

.page-header p {
  color: var(--text-muted);
  margin: 0;
  font-size: 1.1rem;
}

.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 500;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent-2);
  margin-bottom: 10px;
}

.eyebrow::before {
  content: "§";
  font-weight: 700;
}

/* ---------- Nav ---------- */
.site-nav {
  position: sticky;
  top: 0;
  z-index: 20;
  background: var(--bg-elevated);
  border-bottom: 1px solid var(--border);
  box-shadow: 0 1px 0 var(--grid-line);
}

.site-nav-inner {
  max-width: 920px;
  margin: 0 auto;
  padding: 14px 24px;
  display: flex;
  align-items: center;
  gap: 20px;
  flex-wrap: wrap;
}

.site-nav-brand {
  font-family: var(--font-display);
  font-weight: 700;
  letter-spacing: 0.02em;
  color: var(--text) !important;
  text-decoration: none !important;
  white-space: nowrap;
}

.site-nav-links {
  display: flex;
  align-items: center;
  gap: 4px;
  flex-wrap: wrap;
  font-family: var(--font-display);
  font-size: 0.92rem;
  font-weight: 600;
}

.site-nav-group-label {
  font-family: var(--font-mono);
  font-size: 0.66rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-muted);
  font-weight: 500;
  white-space: nowrap;
  margin-right: 2px;
}

.site-nav-divider {
  width: 1px;
  align-self: stretch;
  background: var(--border);
  margin: 2px 8px;
}

.site-nav-links a {
  color: var(--text-muted);
  text-decoration: none !important;
  padding: 6px 10px;
  border-radius: var(--radius-sm);
}

.site-nav-links a:hover {
  background: var(--code-bg);
  color: var(--text);
}

.site-nav-links a.active {
  background: var(--accent);
  color: var(--accent-ink);
}

/* ---------- Cards ---------- */
.card {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
}

.card + .card {
  margin-top: 16px;
}

.card h3 {
  margin-top: 0;
  font-size: 1.15rem;
}

.card li { max-width: 62ch; }

.topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 16px;
  margin-top: 24px;
}

.topic-card {
  position: relative;
  display: block;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px 20px 20px;
  box-shadow: var(--shadow);
  text-decoration: none !important;
  color: var(--text) !important;
  transition: transform 0.15s ease, border-color 0.15s ease;
}

.topic-card::before {
  content: "";
  position: absolute;
  top: 10px;
  left: 10px;
  width: 7px;
  height: 7px;
  border-left: 1.5px solid var(--border);
  border-top: 1.5px solid var(--border);
}

.topic-card:hover {
  transform: translateY(-2px);
  border-color: var(--accent);
}

.topic-card:hover::before { border-color: var(--accent); }

.topic-card .icon {
  font-size: 1.5rem;
  margin-bottom: 10px;
  display: block;
}

.topic-card h3 {
  font-family: var(--font-display);
  margin: 0 0 6px;
  font-size: 1.1rem;
}

.topic-card p {
  margin: 0;
  color: var(--text-muted);
  font-size: 0.92rem;
  font-family: var(--font-body);
}

.topic-card.cross-tag {
  border-style: dashed;
  box-shadow: none;
}

.topic-card.cross-tag:hover {
  border-color: var(--accent-2);
}

.topic-card.cross-tag:hover::before { border-color: var(--accent-2); }

.cross-tag-badge {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.65rem;
  font-weight: 500;
  letter-spacing: 0.03em;
  text-transform: uppercase;
  padding: 2px 7px;
  border-radius: var(--radius-sm);
  background: color-mix(in srgb, var(--accent-2) 14%, transparent);
  color: var(--accent-2);
  margin-bottom: 10px;
}

/* ---------- Panels / logs ---------- */
.panel {
  background: var(--code-bg);
  border: 1px solid var(--code-border);
  border-radius: var(--radius);
  padding: 16px;
  font-family: var(--font-body);
}

.log {
  background: var(--code-bg);
  border: 1px solid var(--code-border);
  border-radius: var(--radius);
  padding: 12px 14px;
  font-family: var(--font-mono);
  font-size: 0.83rem;
  max-height: 260px;
  overflow-y: auto;
}

.log div {
  padding: 3px 0;
  border-bottom: 1px dashed var(--code-border);
}
.log div:last-child { border-bottom: none; }

/* ---------- Buttons / controls ---------- */
.btn {
  appearance: none;
  border: 1px solid var(--border);
  background: var(--bg-elevated);
  color: var(--text);
  padding: 9px 16px;
  border-radius: var(--radius-sm);
  font-family: var(--font-display);
  font-size: 0.88rem;
  font-weight: 600;
  letter-spacing: 0.01em;
  cursor: pointer;
  transition: background 0.15s ease, border-color 0.15s ease;
}

.btn:hover:not(:disabled) {
  border-color: var(--accent);
}

.btn:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

.btn-primary {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--accent-ink);
}

.controls {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
  align-items: center;
  margin: 18px 0;
}

input[type="text"], input[type="number"] {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: var(--radius-sm);
  padding: 9px 12px;
  font-size: 0.95rem;
  font-family: var(--font-mono);
}

input[type="range"] {
  width: 100%;
  accent-color: var(--accent);
}

/* ---------- Badges ---------- */
.badge {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.7rem;
  font-weight: 500;
  padding: 2px 7px;
  border-radius: var(--radius-sm);
  background: var(--code-bg);
  border: 1px solid var(--code-border);
  color: var(--text-muted);
}

.badge-accent {
  background: color-mix(in srgb, var(--accent) 16%, transparent);
  color: var(--accent);
  border-color: transparent;
}

.badge-ok { color: var(--ok); }
.badge-warn { color: var(--warn); }
.badge-danger { color: var(--danger); }

/* ---------- Table ---------- */
table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.92rem;
  font-family: var(--font-body);
}

th, td {
  text-align: left;
  padding: 8px 10px;
  border-bottom: 1px solid var(--border);
}

th {
  font-family: var(--font-mono);
  color: var(--text-muted);
  font-weight: 500;
  font-size: 0.76rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

td.mono, th.mono { font-family: var(--font-mono); font-variant-numeric: tabular-nums; }

/* ---------- Footer nav (prev/next) ---------- */
.page-footer-nav {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  margin-top: 40px;
  padding-top: 20px;
  border-top: 1px solid var(--border);
  font-family: var(--font-display);
  font-size: 0.9rem;
  font-weight: 600;
}

.page-footer-nav a {
  color: var(--text-muted);
}

.page-footer-nav a:hover { color: var(--accent); }

/* ---------- Glossary tooltips ---------- */
.term {
  border-bottom: 1px dotted var(--accent);
  font-weight: 600;
  cursor: help;
  position: relative;
}

.tooltip-popover {
  position: fixed;
  z-index: 100;
  max-width: 320px;
  background: var(--ink);
  color: #ffffff;
  padding: 10px 12px;
  border-radius: var(--radius-sm);
  font-family: var(--font-body);
  font-size: 0.88rem;
  font-weight: 400;
  line-height: 1.5;
  box-shadow: var(--shadow);
  opacity: 0;
  transform: translateY(4px);
  transition: opacity 0.12s ease, transform 0.12s ease;
  pointer-events: none;
}

.tooltip-popover.visible {
  opacity: 1;
  transform: translateY(0);
}

.tooltip-popover .tooltip-arrow {
  position: absolute;
  width: 10px;
  height: 10px;
  background: var(--ink);
  transform: rotate(45deg);
}

.tooltip-popover[data-placement="top"] .tooltip-arrow { bottom: -5px; }
.tooltip-popover[data-placement="bottom"] .tooltip-arrow { top: -5px; }