/* =====================================================================
   TBO CAPSTONE — design tokens
   Palette born from the subject itself: a chalkboard-terminal "ink" base,
   a warm "paper" surface for working panels, and the two states every
   automaton run resolves to — signal (accepted) / alert (rejected).
   ===================================================================== */
:root {
  --ink: #0f1614;
  --ink-soft: #16201d;
  --ink-line: #2a3733;
  --paper: #f5f1e6;
  --paper-dim: #e9e3d3;
  --signal: #4fd1c5;
  --signal-dim: #2e7d74;
  --alert: #e8734a;
  --alert-dim: #9c4a2c;
  --graphite: #8a9290;
  --chalk: #edebe3;
  --chalk-dim: #b9c2be;

  --font-display: "Fraunces", "Iowan Old Style", serif;
  --font-body: "IBM Plex Sans", -apple-system, sans-serif;
  --font-mono: "IBM Plex Mono", ui-monospace, monospace;

  --radius: 3px;
  --shadow-panel: 0 1px 0 rgba(0, 0, 0, 0.4);
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--ink);
  color: var(--chalk);
  font-family: var(--font-body);
  font-size: 15px;
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
}

h1, h2, h3, h4 {
  font-family: var(--font-display);
  font-weight: 600;
  color: var(--chalk);
  margin: 0 0 0.5em 0;
  letter-spacing: -0.01em;
}

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

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

:focus-visible {
  outline: 2px solid var(--signal);
  outline-offset: 2px;
}

@media (prefers-reduced-motion: reduce) {
  * { animation: none !important; transition: none !important; }
}

/* ---------------------------------------------------------------------
   Layout shell
   --------------------------------------------------------------------- */
.site-header {
  border-bottom: 1px solid var(--ink-line);
  background: linear-gradient(180deg, var(--ink-soft), var(--ink));
  position: sticky;
  top: 0;
  z-index: 20;
}

.header-inner {
  max-width: 1120px;
  margin: 0 auto;
  padding: 14px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  flex-wrap: wrap;
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  color: var(--chalk);
  font-family: var(--font-display);
  font-weight: 600;
  font-size: 1.05rem;
}

.brand-mark {
  width: 26px; height: 26px;
  border-radius: 50%;
  border: 2px solid var(--signal);
  box-shadow: 0 0 0 3px var(--ink), 0 0 0 4px var(--signal-dim);
  flex-shrink: 0;
}

.state-nav { display: flex; align-items: center; gap: 4px; flex-wrap: wrap; }

.state-nav a {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  padding: 6px 12px 6px 8px;
  border-radius: 999px;
  border: 1.5px solid var(--ink-line);
  color: var(--chalk-dim);
  font-size: 0.82rem;
  font-family: var(--font-mono);
  text-decoration: none;
  transition: border-color 0.15s ease, color 0.15s ease, background 0.15s ease;
}

.state-nav a .dot {
  width: 9px; height: 9px; border-radius: 50%;
  border: 1.5px solid currentColor;
}

.state-nav a:hover { border-color: var(--signal-dim); color: var(--chalk); }

.state-nav a.is-active {
  border-color: var(--signal);
  color: var(--ink);
  background: var(--signal);
  font-weight: 600;
}
.state-nav a.is-active .dot { background: var(--ink); }

main { max-width: 1120px; margin: 0 auto; padding: 40px 24px 80px; }

.site-footer {
  border-top: 1px solid var(--ink-line);
  padding: 28px 24px 40px;
  text-align: center;
  color: var(--graphite);
  font-size: 0.82rem;
}
.site-footer .mono { color: var(--chalk-dim); }

/* ---------------------------------------------------------------------
   Hero (home)
   --------------------------------------------------------------------- */
.eyebrow {
  font-family: var(--font-mono);
  text-transform: uppercase;
  letter-spacing: 0.14em;
  font-size: 0.72rem;
  color: var(--signal);
  margin-bottom: 14px;
}

.hero h1 {
  font-size: clamp(2.1rem, 4.4vw, 3.4rem);
  max-width: 15ch;
  line-height: 1.06;
}

.hero p.lede {
  max-width: 56ch;
  color: var(--chalk-dim);
  font-size: 1.05rem;
}

.automaton-diagram { margin: 48px 0 8px; }
.automaton-diagram svg { width: 100%; height: auto; display: block; }

.automaton-diagram .state-circle {
  fill: var(--ink-soft);
  stroke: var(--chalk-dim);
  stroke-width: 1.6;
  transition: stroke 0.15s ease, fill 0.15s ease;
}
.automaton-diagram a:hover .state-circle { stroke: var(--signal); fill: var(--ink-line); }
.automaton-diagram .state-circle-inner { fill: none; stroke: var(--signal); stroke-width: 1.6; }
.automaton-diagram .state-label {
  fill: var(--chalk);
  font-family: var(--font-mono);
  font-size: 12.5px;
  text-anchor: middle;
}
.automaton-diagram .state-sub {
  fill: var(--chalk-dim);
  font-family: var(--font-mono);
  font-size: 9.5px;
  text-anchor: middle;
}
.automaton-diagram .edge-path { fill: none; stroke: var(--ink-line); stroke-width: 1.4; marker-end: url(#arrowhead); }
.automaton-diagram .start-arrow { fill: none; stroke: var(--signal); stroke-width: 1.4; marker-end: url(#arrowhead-signal); }

/* ---------------------------------------------------------------------
   Cards
   --------------------------------------------------------------------- */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(230px, 1fr));
  gap: 16px;
  margin-top: 20px;
}

.module-card {
  background: var(--ink-soft);
  border: 1px solid var(--ink-line);
  border-radius: var(--radius);
  padding: 20px;
  display: flex;
  flex-direction: column;
  gap: 10px;
  transition: border-color 0.15s ease, transform 0.15s ease;
}
.module-card:hover { border-color: var(--signal-dim); transform: translateY(-2px); }

.module-card .idx { font-family: var(--font-mono); color: var(--signal); font-size: 0.78rem; }
.module-card h3 { font-size: 1.15rem; }
.module-card p { color: var(--chalk-dim); font-size: 0.88rem; margin: 0; }
.module-card .cpmk { font-family: var(--font-mono); font-size: 0.72rem; color: var(--graphite); margin-top: auto; }

/* ---------------------------------------------------------------------
   Module page shell
   --------------------------------------------------------------------- */
.module-header { margin-bottom: 28px; }
.module-header h1 { font-size: 1.9rem; }
.module-header p { color: var(--chalk-dim); max-width: 64ch; }

.tabs { display: flex; gap: 6px; flex-wrap: wrap; border-bottom: 1px solid var(--ink-line); margin-bottom: 24px; }
.tab-btn {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  background: none;
  border: none;
  color: var(--chalk-dim);
  padding: 10px 16px;
  cursor: pointer;
  border-bottom: 2px solid transparent;
  transition: color 0.15s ease, border-color 0.15s ease;
}
.tab-btn:hover { color: var(--chalk); }
.tab-btn.is-active { color: var(--signal); border-color: var(--signal); }
.tab-panel { display: none; }
.tab-panel.is-active { display: block; }

.panel-grid {
  display: grid;
  grid-template-columns: minmax(280px, 1fr) minmax(320px, 1.3fr);
  gap: 24px;
  align-items: start;
}
@media (max-width: 860px) { .panel-grid { grid-template-columns: 1fr; } }

.panel {
  background: var(--ink-soft);
  border: 1px solid var(--ink-line);
  border-radius: var(--radius);
  padding: 20px;
}
.panel h2, .panel h3 { font-size: 1rem; font-family: var(--font-mono); color: var(--chalk-dim); text-transform: uppercase; letter-spacing: 0.06em; margin-bottom: 14px; }

/* ---------------------------------------------------------------------
   Forms
   --------------------------------------------------------------------- */
.field { margin-bottom: 16px; }
.field label {
  display: block;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  color: var(--chalk-dim);
  margin-bottom: 6px;
}
.field .hint { font-size: 0.74rem; color: var(--graphite); margin-top: 5px; }

input[type="text"], textarea, select {
  width: 100%;
  background: var(--ink);
  border: 1px solid var(--ink-line);
  color: var(--chalk);
  padding: 9px 11px;
  border-radius: var(--radius);
  font-family: var(--font-mono);
  font-size: 0.88rem;
}
textarea { resize: vertical; min-height: 90px; line-height: 1.5; }
input[type="text"]:focus, textarea:focus, select:focus { border-color: var(--signal); }

.field-row { display: flex; gap: 12px; }
.field-row .field { flex: 1; }

button.btn {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  background: var(--signal);
  color: var(--ink);
  border: none;
  padding: 10px 18px;
  border-radius: var(--radius);
  cursor: pointer;
  font-weight: 600;
  transition: background 0.15s ease, transform 0.1s ease;
}
button.btn:hover { background: #6fe0d5; }
button.btn:active { transform: translateY(1px); }
button.btn.secondary {
  background: transparent;
  color: var(--chalk);
  border: 1px solid var(--ink-line);
  font-weight: 400;
}
button.btn.secondary:hover { border-color: var(--signal-dim); background: var(--ink-line); }
.btn-row { display: flex; gap: 10px; flex-wrap: wrap; margin-top: 18px; }

/* ---------------------------------------------------------------------
   Results
   --------------------------------------------------------------------- */
.result-banner {
  font-family: var(--font-mono);
  padding: 12px 16px;
  border-radius: var(--radius);
  margin-bottom: 16px;
  font-size: 0.92rem;
  display: flex;
  align-items: center;
  gap: 10px;
  border: 1px solid transparent;
}
.result-banner.accept { background: rgba(79, 209, 197, 0.12); border-color: var(--signal-dim); color: var(--signal); }
.result-banner.reject { background: rgba(232, 115, 74, 0.12); border-color: var(--alert-dim); color: var(--alert); }
.result-banner .badge {
  width: 10px; height: 10px; border-radius: 50%; background: currentColor; flex-shrink: 0;
}

.error-banner {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  padding: 12px 16px;
  border-radius: var(--radius);
  background: rgba(232, 115, 74, 0.1);
  border: 1px solid var(--alert-dim);
  color: var(--alert);
  margin-bottom: 16px;
}

.empty-state {
  color: var(--graphite);
  font-size: 0.85rem;
  font-family: var(--font-mono);
  padding: 24px 0;
  text-align: center;
}

table.trace-table {
  width: 100%;
  border-collapse: collapse;
  font-family: var(--font-mono);
  font-size: 0.82rem;
  margin-bottom: 8px;
}
table.trace-table th, table.trace-table td {
  text-align: left;
  padding: 7px 10px;
  border-bottom: 1px solid var(--ink-line);
}
table.trace-table th { color: var(--chalk-dim); font-weight: 400; text-transform: uppercase; font-size: 0.7rem; letter-spacing: 0.05em; }
table.trace-table tr:last-child td { border-bottom: none; }
.scroll-x { overflow-x: auto; }

.graph-canvas {
  width: 100%;
  height: 320px;
  background: var(--ink);
  border: 1px solid var(--ink-line);
  border-radius: var(--radius);
}

.derivation-lines {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  line-height: 1.9;
}
.derivation-lines .arrow { color: var(--graphite); margin: 0 8px; }
.derivation-lines .step-tag { color: var(--signal); font-size: 0.72rem; margin-right: 8px; }

.grammar-block {
  font-family: var(--font-mono);
  font-size: 0.86rem;
  line-height: 1.9;
  background: var(--ink);
  border: 1px solid var(--ink-line);
  border-radius: var(--radius);
  padding: 14px 16px;
}
.grammar-block .nt { color: var(--signal); }

.section-title {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--chalk-dim);
  margin: 22px 0 10px;
}
.section-title:first-child { margin-top: 0; }

.step-card {
  border: 1px solid var(--ink-line);
  border-radius: var(--radius);
  padding: 14px 16px;
  margin-bottom: 12px;
  background: var(--ink);
}
.step-card h4 { font-size: 0.92rem; color: var(--signal); margin-bottom: 4px; font-family: var(--font-mono); }
.step-card .desc { color: var(--chalk-dim); font-size: 0.82rem; margin-bottom: 10px; }

.pill {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  padding: 3px 9px;
  border-radius: 999px;
  border: 1px solid var(--ink-line);
  color: var(--chalk-dim);
}
.pill.type-highlight { border-color: var(--signal); color: var(--signal); }

/* ---------------------------------------------------------------------
   Parse tree (pure-CSS org-chart pattern)
   --------------------------------------------------------------------- */
.tree-wrap { overflow-x: auto; padding: 20px 10px; }
ul.tree, ul.tree ul {
  list-style: none;
  margin: 0; padding: 0;
  display: flex;
  justify-content: center;
}
ul.tree { padding-top: 0; }
ul.tree ul { padding-top: 28px; position: relative; }
ul.tree li {
  display: flex;
  flex-direction: column;
  align-items: center;
  position: relative;
  padding: 0 10px;
}
ul.tree ul li { padding-top: 0; }
ul.tree ul::before {
  content: '';
  position: absolute;
  top: 0; left: 50%;
  border-left: 1.5px solid var(--ink-line);
  height: 28px;
}
ul.tree li li::before {
  content: '';
  position: absolute;
  top: -28px; left: 50%; right: 50%;
  border-top: 1.5px solid var(--ink-line);
  height: 28px;
}
ul.tree li li:first-child::before { left: 50%; right: 50%; }
ul.tree > li > ul > li::before { border-left: 1.5px solid var(--ink-line); }
.tree-row { display: flex; }
.tree-row > li:not(:only-child)::before {
  content: '';
  position: absolute;
  top: -28px; height: 28px;
  border-top: 1.5px solid var(--ink-line);
  left: 0; right: 0;
}
.tree-row > li:first-child:not(:only-child)::before { left: 50%; }
.tree-row > li:last-child:not(:only-child)::before { right: 50%; }

.tree-node {
  font-family: var(--font-mono);
  font-size: 0.82rem;
  border: 1.5px solid var(--chalk-dim);
  border-radius: 50%;
  min-width: 34px; height: 34px;
  display: flex; align-items: center; justify-content: center;
  padding: 0 6px;
  background: var(--ink-soft);
  color: var(--chalk);
  z-index: 1;
  white-space: nowrap;
}
.tree-node.is-terminal { border-radius: var(--radius); border-color: var(--signal-dim); color: var(--signal); background: rgba(79,209,197,0.08); }
.tree-node.is-epsilon { border-color: var(--graphite); color: var(--graphite); font-style: italic; }

/* ---------------------------------------------------------------------
   Utility
   --------------------------------------------------------------------- */
.stack-flow { font-family: var(--font-mono); font-size: 0.8rem; }
.stack-flow .action-EXPAND { color: var(--signal); }
.stack-flow .action-MATCH { color: var(--chalk-dim); }

.two-col { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; }
@media (max-width: 760px) { .two-col { grid-template-columns: 1fr; } }

.page-404 { text-align: center; padding: 80px 20px; }