/* ──────────────────────────────────────────────────────────────────────────
   Coupled Logistic Map — Dark Theme
   ────────────────────────────────────────────────────────────────────────── */

/* ── Custom Properties ─────────────────────────────────────────────────── */
:root {
  --bg:         #0d0d0f;
  --surface:    #16161a;
  --surface2:   #1e1e24;
  --border:     #2a2a35;
  --accent:     #7c6af7;
  --accent-dim: #4a3fa0;
  --warm:       #f07040;
  --green:      #4ecb6e;
  --text:       #e8e8f0;
  --text-muted: #888899;
  --text-dim:   #555566;
  --radius:     6px;
  --radius-lg:  10px;
  --font:       'Inter', system-ui, sans-serif;
  --mono:       'Inter', ui-monospace, monospace;
}

/* ── Reset ──────────────────────────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { font-size: 15px; }
body {
  background: var(--bg);
  color: var(--text);
  font-family: var(--font);
  line-height: 1.5;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ambient glow — more visible, centered behind canvas area */
body::before {
  content: '';
  position: fixed;
  inset: 0;
  pointer-events: none;
  background:
    radial-gradient(ellipse 60% 70% at 50% 46%, rgba(124,106,247,0.10) 0%, transparent 70%),
    radial-gradient(ellipse 35% 40% at 12% 50%,  rgba(124,106,247,0.07) 0%, transparent 100%),
    radial-gradient(ellipse 30% 35% at 90% 10%,  rgba(240,112,64,0.05) 0%, transparent 100%),
    radial-gradient(ellipse 25% 30% at 88% 90%,  rgba(78,203,110,0.03) 0%, transparent 100%);
  z-index: 0;
}
body > * { position: relative; z-index: 1; }

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

/* ── Header ─────────────────────────────────────────────────────────────── */
.site-header {
  border-bottom: 1px solid rgba(255,255,255,0.05);
  padding: 10px 24px;
  flex-shrink: 0;
  background: rgba(13,13,15,0.7);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
}
.header-inner {
  max-width: 1400px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}
.site-header h1 {
  font-size: 1.18rem;
  font-weight: 700;
  letter-spacing: -0.03em;
  background: linear-gradient(95deg, var(--text) 55%, var(--accent));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.subtitle {
  font-size: 0.74rem;
  color: var(--text-muted);
  margin-top: 2px;
  letter-spacing: 0.01em;
}

/* ── Main Grid ───────────────────────────────────────────────────────────── */
/*  3 explicit columns — hardcoded to avoid CSS-variable resolution bugs    */
.app-grid {
  max-width: 1400px;
  margin: 0 auto;
  padding: 12px 20px;
  display: grid;
  grid-template-columns: 316px 1fr 316px;
  grid-template-areas: "tour canvas controls";
  gap: 16px;
  flex: 1;
  width: 100%;
  align-items: start;
  transition: grid-template-columns 0.25s ease;
}

/* Collapsed states — direct values, no CSS vars */
.app-grid.tour-collapsed                        { grid-template-columns:  44px 1fr 316px; }
.app-grid.controls-collapsed                    { grid-template-columns: 316px 1fr  44px; }
.app-grid.tour-collapsed.controls-collapsed     { grid-template-columns:  44px 1fr  44px; }

/* ── Tour Column (left) ──────────────────────────────────────────────────── */
.tour-col {
  grid-area: tour;
  display: flex;
  flex-direction: column;
  gap: 12px;
  background: rgba(22,22,26,0.75);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border: 1px solid rgba(255,255,255,0.06);
  border-radius: var(--radius-lg);
  padding: 14px;
  overflow: hidden;
  max-height: calc(100dvh - 60px);
  align-self: start;
  position: sticky;
  top: 10px;
  box-shadow: 0 4px 24px rgba(0,0,0,0.35), inset 0 1px 0 rgba(255,255,255,0.04);
}

/* inner scroll region — only the middle part scrolls */
.tour-scroll {
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: 12px;
  overflow-y: auto;
  overflow-x: hidden;
  min-height: 0;
}
.tour-scroll::-webkit-scrollbar { width: 4px; }
.tour-scroll::-webkit-scrollbar-track { background: transparent; }
.tour-scroll::-webkit-scrollbar-thumb { background: var(--border); border-radius: 10px; }

/* collapsed state */
.tour-col.collapsed {
  padding: 10px 6px;
}
.tour-col.collapsed .tour-scroll,
.tour-col.collapsed .tour-footer,
.tour-col.collapsed .tour-col-hint {
  display: none;
}
.tour-col.collapsed .tour-col-header {
  border-bottom: none;
  padding-bottom: 0;
}
.tour-col.collapsed .tour-col-labels { display: none; }

.tour-col-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 6px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border);
  flex-shrink: 0;
}
.tour-col-labels {
  display: flex;
  flex-direction: column;
  gap: 2px;
  min-width: 0;
}
.tour-col-title {
  font-size: 0.72rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--text-dim);
}
.tour-col-hint {
  font-size: 0.75rem;
  color: var(--text-muted);
  font-style: italic;
}

/* ── Sidebar Toggle Buttons ─────────────────────────────────────────────── */
.sidebar-toggle {
  background: none;
  border: 1px solid transparent;
  color: var(--text-dim);
  font-size: 0.9rem;
  line-height: 1;
  cursor: pointer;
  width: 24px; height: 24px;
  display: flex; align-items: center; justify-content: center;
  border-radius: var(--radius);
  flex-shrink: 0;
  transition: color 0.15s, background 0.15s, border-color 0.15s;
}
.sidebar-toggle:hover { color: var(--text); background: var(--surface2); border-color: var(--border); }
.sidebar-toggle-right { margin-right: 4px; }

/* ── Canvas Column (center) ─────────────────────────────────────────────── */
.canvas-col {
  grid-area: canvas;
  display: flex;
  flex-direction: column;
  gap: 10px;
  min-width: 0;
}

.canvas-container {
  position: relative;
  /* constrain by both column width and viewport height so canvas never scrolls off-screen */
  width: min(100%, calc(100dvh - 310px));
  aspect-ratio: 1 / 1;
  margin: 0 auto;
  border-radius: var(--radius-lg);
  overflow: hidden;
  border: 1px solid rgba(124,106,247,0.25);
  cursor: crosshair;
  background: #000;
  box-shadow:
    0 0 0 1px rgba(124,106,247,0.06),
    0 0 80px rgba(124,106,247,0.22),
    0 0 180px rgba(124,106,247,0.08),
    0 8px 40px rgba(0,0,0,0.65);
  transition: box-shadow 0.3s ease;
}
.canvas-container:hover {
  box-shadow:
    0 0 0 1px rgba(124,106,247,0.12),
    0 0 100px rgba(124,106,247,0.28),
    0 0 200px rgba(124,106,247,0.10),
    0 8px 40px rgba(0,0,0,0.65);
}
.canvas-container canvas {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  image-rendering: pixelated;
  image-rendering: crisp-edges;
}
#overlay-canvas { pointer-events: none; }

/* Playback bar */
.playback-bar {
  display: flex;
  align-items: center;
  gap: 8px;
}
.hud-t {
  font-family: var(--mono);
  font-size: 0.75rem;
  color: var(--text-dim);
}

/* ── Live Pulse Dot ─────────────────────────────────────────────────────── */
.live-dot {
  width: 7px; height: 7px;
  border-radius: 50%;
  background: var(--green);
  flex-shrink: 0;
  margin-left: auto;
  animation: livepulse 2s ease-in-out infinite;
}
.live-dot.paused {
  animation: none;
  background: var(--text-dim);
}
@keyframes livepulse {
  0%, 100% { opacity: 1;    transform: scale(1); }
  50%       { opacity: 0.3; transform: scale(0.6); }
}

/* Status line */
.status-line {
  font-size: 0.8rem;
  color: var(--text-muted);
  min-height: 1.4em;
  font-style: italic;
}

/* Metrics chart */
.metrics-wrap {
  position: relative;
  border: 1px solid rgba(255,255,255,0.05);
  border-radius: var(--radius);
  background: rgba(22,22,26,0.6);
  overflow: hidden;
  backdrop-filter: blur(8px);
}
#metrics-canvas {
  display: block;
  width: 100%;
  height: 80px;
}
/* Overlay labels — pinned to left edge of each chart half */
.metrics-labels {
  position: absolute;
  top: 0; left: 0;
  width: 70px;
  height: 100%;
  display: flex;
  flex-direction: column;
  justify-content: space-around;
  padding: 6px 0 6px 6px;
  pointer-events: none;
}
.ml-sync, .ml-disagree {
  font-size: 0.6rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  opacity: 0.65;
  line-height: 1;
}
.ml-sync     { color: var(--green); }
.ml-disagree { color: var(--warm); }

/* ── Controls Column (right) ────────────────────────────────────────────── */
.controls-col {
  grid-area: controls;
  display: flex;
  flex-direction: column;
  gap: 0;
  background: rgba(22,22,26,0.75);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border: 1px solid rgba(255,255,255,0.06);
  border-radius: var(--radius-lg);
  overflow: hidden;
  align-self: start;
  position: sticky;
  top: 10px;
  min-width: 0;
  box-shadow: 0 4px 24px rgba(0,0,0,0.35), inset 0 1px 0 rgba(255,255,255,0.04);
}

.controls-col.collapsed .tab-panel   { display: none; }
.controls-col.collapsed .tab-btn     { display: none; }
.controls-col.collapsed .tab-bar     { border-bottom: none; justify-content: center; }

/* ── Tab Bar ────────────────────────────────────────────────────────────── */
.tab-bar {
  display: flex;
  align-items: center;
  border-bottom: 1px solid var(--border);
}
.tab-btn {
  flex: 1;
  padding: 10px 0;
  background: none;
  border: none;
  color: var(--text-muted);
  font-size: 0.82rem;
  font-weight: 500;
  cursor: pointer;
  transition: color 0.15s, background 0.15s;
}
.tab-btn:hover { color: var(--text); background: var(--surface2); }
.tab-btn.active {
  color: var(--accent);
  background: rgba(124,106,247,0.08);
  border-bottom: 2px solid var(--accent);
  margin-bottom: -1px;
  text-shadow: 0 0 20px rgba(124,106,247,0.5);
}

/* ── Tab Panels ─────────────────────────────────────────────────────────── */
.tab-panel {
  padding: 12px;
  display: flex;
  flex-direction: column;
  gap: 10px;
  max-height: calc(100dvh - 116px);
  overflow-y: auto;
}
.tab-panel.hidden { display: none; }
.tab-panel::-webkit-scrollbar { width: 4px; }
.tab-panel::-webkit-scrollbar-track { background: transparent; }
.tab-panel::-webkit-scrollbar-thumb { background: var(--border); border-radius: 10px; }

/* ── Field Groups ───────────────────────────────────────────────────────── */
.field-group {
  border: 1px solid rgba(255,255,255,0.05);
  border-radius: var(--radius);
  padding: 10px 10px 8px;
  display: flex;
  flex-direction: column;
  gap: 8px;
  background: rgba(255,255,255,0.02);
}
.field-desc {
  font-size: 0.72rem;
  color: var(--text-dim);
  line-height: 1.5;
  font-style: italic;
  margin-bottom: 2px;
}

.field-group legend {
  font-size: 0.65rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.09em;
  color: var(--text-dim);
  padding: 0 6px;
}

/* ── Slider Rows ────────────────────────────────────────────────────────── */
.slider-row {
  display: grid;
  grid-template-columns: 90px 1fr 46px;
  align-items: center;
  gap: 6px;
}
.slider-row label {
  font-size: 0.83rem;
  color: var(--text);
  white-space: nowrap;
}
.param-hint {
  font-size: 0.7rem;
  color: var(--text-dim);
  font-style: italic;
  font-weight: 400;
}

input[type="range"] {
  -webkit-appearance: none;
  appearance: none;
  width: 100%;
  height: 4px;
  background: var(--border);
  border-radius: 2px;
  outline: none;
  cursor: pointer;
}
input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  width: 14px; height: 14px;
  border-radius: 50%;
  background: var(--accent);
  cursor: pointer;
  transition: transform 0.1s, box-shadow 0.15s;
  box-shadow: 0 0 0 0 rgba(124,106,247,0);
}
input[type="range"]:hover::-webkit-slider-thumb,
input[type="range"]:focus::-webkit-slider-thumb {
  transform: scale(1.2);
  box-shadow: 0 0 0 4px rgba(124,106,247,0.2), 0 0 12px rgba(124,106,247,0.35);
}
input[type="range"]::-moz-range-thumb {
  width: 14px; height: 14px; border-radius: 50%;
  background: var(--accent); border: none; cursor: pointer;
}

.val-badge {
  font-family: var(--mono);
  font-size: 0.75rem;
  color: var(--accent);
  text-align: right;
}

/* ── Select Rows ────────────────────────────────────────────────────────── */
.select-row {
  display: grid;
  grid-template-columns: 90px 1fr;
  align-items: center;
  gap: 6px;
}
.select-row label { font-size: 0.83rem; color: var(--text); }

select {
  background: var(--surface2);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 4px 6px;
  font-size: 0.8rem;
  font-family: var(--font);
  cursor: pointer;
  outline: none;
  width: 100%;
}
select:focus { border-color: var(--accent); }

/* ── Buttons ────────────────────────────────────────────────────────────── */
.icon-btn {
  background: rgba(30,30,36,0.8);
  border: 1px solid rgba(255,255,255,0.07);
  color: var(--text-muted);
  border-radius: var(--radius);
  width: 34px; height: 34px;
  font-size: 1rem;
  cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  transition: background 0.15s, border-color 0.2s, transform 0.1s, color 0.15s, box-shadow 0.2s;
  flex-shrink: 0;
}
.icon-btn:hover {
  background: rgba(124,106,247,0.12);
  border-color: rgba(124,106,247,0.5);
  color: var(--accent);
  transform: scale(1.08);
  box-shadow: 0 0 12px rgba(124,106,247,0.2);
}

/* ── Tool Grid ──────────────────────────────────────────────────────────── */
.tool-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 5px;
}
.tool-btn {
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--text-muted);
  border-radius: var(--radius);
  padding: 6px 4px;
  font-size: 0.75rem;
  cursor: pointer;
  text-align: center;
  transition: background 0.12s, color 0.12s, border-color 0.12s;
}
.tool-btn:hover  { color: var(--text); border-color: var(--accent-dim); }
.tool-btn.active {
  background: rgba(124,106,247,0.18);
  border-color: rgba(124,106,247,0.55);
  color: #fff;
  font-weight: 600;
  box-shadow: 0 0 10px rgba(124,106,247,0.15);
}

/* ── Shape Buttons ──────────────────────────────────────────────────────── */
.shape-row { display: flex; align-items: center; gap: 6px; }
.shape-btn {
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--text-muted);
  border-radius: var(--radius);
  width: 34px; height: 34px;
  font-size: 1rem;
  cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  transition: background 0.12s, border-color 0.12s, color 0.12s;
}
.shape-btn:hover  { color: var(--text); border-color: var(--accent-dim); }
.shape-btn.active { background: var(--accent-dim); border-color: var(--accent); color: #fff; }
.brush-preview {
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface2);
  margin-left: auto;
}

/* ── Custom Colormap ────────────────────────────────────────────────────── */
.custom-colors {
  display: flex; gap: 10px; align-items: center;
  font-size: 0.8rem;
}
.custom-colors input[type="color"] {
  width: 36px; height: 24px;
  border: 1px solid var(--border); border-radius: 4px;
  cursor: pointer; padding: 1px; background: var(--surface2);
}

/* ── Preset Buttons ─────────────────────────────────────────────────────── */
.preset-buttons { display: flex; flex-wrap: wrap; gap: 5px; }
.preset-btn {
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--text-muted);
  border-radius: var(--radius);
  padding: 4px 9px;
  font-size: 0.75rem;
  cursor: pointer;
  transition: background 0.12s, color 0.12s, border-color 0.12s;
}
.preset-btn:hover { background: var(--accent-dim); border-color: var(--accent); color: #fff; }

/* ── Chapter Nav — vertical stepper ────────────────────────────────────── */
.chapter-nav {
  display: flex;
  flex-direction: column;   /* MUST be column for left-sidebar layout */
  gap: 3px;
}
.chapter-btn {
  background: transparent;
  border: 1px solid transparent;
  color: var(--text-muted);
  border-radius: var(--radius);
  padding: 7px 8px;
  font-size: 0.81rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 8px;
  text-align: left;
  width: 100%;
  transition: background 0.12s, border-color 0.12s, color 0.12s;
}
.chapter-btn:hover { color: var(--text); background: var(--surface2); border-color: var(--border); }
.chapter-btn.active {
  background: rgba(124,106,247,0.15);
  border-color: rgba(124,106,247,0.5);
  color: #fff;
  box-shadow: inset 0 0 0 1px rgba(124,106,247,0.2);
}

.ch-num {
  background: var(--border);
  border-radius: 50%;
  width: 20px; height: 20px;
  display: flex; align-items: center; justify-content: center;
  font-size: 0.68rem; font-weight: 700;
  flex-shrink: 0;
}
.chapter-btn.active .ch-num { background: rgba(255,255,255,0.2); }
.ch-title { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; min-width: 0; }

/* ── Tour Narrative ─────────────────────────────────────────────────────── */
.tour-narrative-wrap { min-height: 0; }

.chapter-narrative {
  font-size: 0.85rem;
  line-height: 1.65;
  color: var(--text);
  transition: opacity 0.18s ease;
}
.chapter-narrative h3 {
  font-size: 0.92rem; font-weight: 600;
  margin-bottom: 8px; color: var(--accent);
}
.chapter-narrative p { margin-bottom: 8px; }
.chapter-narrative .aside {
  color: var(--text-muted);
  font-style: italic;
  border-left: 2px solid var(--accent-dim);
  padding-left: 10px;
}
.chapter-narrative code {
  font-family: var(--mono);
  font-size: 0.85em;
  background: var(--surface2);
  padding: 1px 5px;
  border-radius: 3px;
  color: var(--warm);
}
.placeholder { color: var(--text-dim); font-style: italic; }

.tour-footer {
  display: flex;
  gap: 6px;
  padding-top: 8px;
  border-top: 1px solid var(--border);
  flex-shrink: 0;
}
.nav-btn {
  flex: 1;
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--text-muted);
  border-radius: var(--radius);
  padding: 7px 10px;
  font-size: 0.78rem;
  cursor: pointer;
  transition: background 0.12s, color 0.12s, border-color 0.12s;
}
.nav-btn:hover:not(:disabled) { background: var(--accent-dim); border-color: var(--accent); color: #fff; }
.nav-btn:disabled { opacity: 0.3; cursor: not-allowed; }

/* ── Collapsible Panels ─────────────────────────────────────────────────── */
.collapsible-panel {
  max-width: 1400px;
  margin: 0 auto 12px;
  width: calc(100% - 40px);
  border: 1px solid rgba(255,255,255,0.05);
  border-radius: var(--radius-lg);
  background: rgba(22,22,26,0.7);
  backdrop-filter: blur(12px);
  overflow: hidden;
}
.collapsible-panel summary {
  display: flex; align-items: center; gap: 10px;
  padding: 10px 14px;
  cursor: pointer; list-style: none; user-select: none;
  transition: background 0.15s;
}
.collapsible-panel summary::-webkit-details-marker { display: none; }
.collapsible-panel summary::before {
  content: '▶'; font-size: 0.6rem; color: var(--text-dim);
  transition: transform 0.2s; flex-shrink: 0;
}
.collapsible-panel[open] summary::before { transform: rotate(90deg); }
.collapsible-panel summary:hover { background: var(--surface2); }

.panel-title  { font-size: 0.88rem; font-weight: 600; color: var(--text); }
.panel-hint   { font-size: 0.75rem; color: var(--text-dim); font-style: italic; }

/* ── Bifurcation Diagram ────────────────────────────────────────────────── */
.bif-body {
  border-top: 1px solid var(--border);
  padding: 12px 16px 14px;
  display: flex; flex-direction: column; gap: 8px;
}
#bifurcation-canvas {
  display: block; width: 100%; height: 180px;
  border-radius: var(--radius); border: 1px solid var(--border);
}
.bif-caption { font-size: 0.75rem; color: var(--text-dim); font-style: italic; }

/* ── Help Overlay ───────────────────────────────────────────────────────── */
.help-overlay {
  position: fixed; inset: 0;
  background: rgba(0,0,0,0.65);
  display: flex; align-items: center; justify-content: center;
  z-index: 100; backdrop-filter: blur(4px);
}
.help-overlay.hidden { display: none; }
.help-box {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius-lg); padding: 24px;
  min-width: 300px; position: relative;
}
.help-box h2 { font-size: 1rem; margin-bottom: 14px; color: var(--text); }
.help-close {
  position: absolute; top: 12px; right: 12px;
  background: none; border: none; color: var(--text-muted);
  font-size: 1rem; cursor: pointer;
}
.help-close:hover { color: var(--text); }
.shortcut-table { border-collapse: collapse; width: 100%; }
.shortcut-table td {
  padding: 5px 8px; font-size: 0.82rem;
  border-bottom: 1px solid var(--border);
}
.shortcut-table td:first-child {
  font-family: var(--mono); color: var(--accent);
  white-space: nowrap; width: 80px;
}
.shortcut-table tr:last-child td { border-bottom: none; }

/* ── Footer ─────────────────────────────────────────────────────────────── */
.site-footer {
  border-top: 1px solid rgba(255,255,255,0.04);
  padding: 9px 24px;
  text-align: center;
  font-size: 0.72rem;
  color: var(--text-dim);
  flex-shrink: 0;
}

/* ── About Section ──────────────────────────────────────────────────────── */
.about-section {
  max-width: 1400px;
  margin: 0 auto 24px;
  width: calc(100% - 40px);
  border: 1px solid rgba(255,255,255,0.05);
  border-radius: var(--radius-lg);
  background: rgba(22,22,26,0.7);
  backdrop-filter: blur(12px);
  overflow: hidden;
}

.about-inner {
  padding: 28px 32px 32px;
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.about-header h2 {
  font-size: 1.15rem;
  font-weight: 600;
  color: var(--text);
  margin-bottom: 6px;
  letter-spacing: -0.02em;
}

.about-lead {
  font-size: 0.9rem;
  color: var(--text-muted);
  font-style: italic;
}

.about-cols {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 40px;
}

.about-col h3 {
  font-size: 0.78rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--accent);
  margin-bottom: 14px;
}

.about-col p {
  font-size: 0.875rem;
  line-height: 1.75;
  color: var(--text);
  margin-bottom: 12px;
}

.about-col p:last-child { margin-bottom: 0; }

.about-col a { color: var(--accent); }
.about-col a:hover { text-decoration: underline; }

/* rendered KaTeX block equations */
.math-block {
  margin: 14px 0;
  text-align: center;
  overflow-x: auto;
  padding: 4px 0;
}

/* ── Responsive — stack on small screens only ───────────────────────────── */
@media (max-width: 700px) {
  .app-grid {
    grid-template-columns: 1fr !important;
    grid-template-areas:
      "canvas"
      "tour"
      "controls";
    padding: 12px;
    gap: 12px;
  }
  .tour-col, .controls-col { position: static; max-height: none; }
  .collapsible-panel { width: calc(100% - 24px); }
  .sidebar-toggle { display: none; }
  .about-section { width: calc(100% - 24px); }
  .about-cols { grid-template-columns: 1fr; gap: 24px; }
  .about-inner { padding: 20px 18px 24px; }
}