:root {
  --bg: #f4f6f9;
  --panel-bg: #ffffff;
  --border: #d7dce3;
  --text: #1c2430;
  --muted: #6b7684;
  --accent: #2563eb;
  --accent-hover: #1d4ed8;
  --n-region: #dbe8ff;
  --p-region: #ffe0e0;
  --depletion: #4b5563;
  --electron: #2563eb;
  --hole: #dc2626;
  --ion-plus: #64748b;
  --ion-minus: #64748b;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #12161c;
    --panel-bg: #1a2029;
    --border: #2b3340;
    --text: #e6eaf0;
    --muted: #93a0b0;
    --accent: #4d8dff;
    --accent-hover: #6ea0ff;
    --n-region: #1b2740;
    --p-region: #3a1f22;
    --depletion: #8a94a3;
    --electron: #5b9dff;
    --hole: #ff6b6b;
    --ion-plus: #9aa5b3;
    --ion-minus: #9aa5b3;
  }
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  height: 100%;
  background: var(--bg);
  color: var(--text);
  font-family: "Segoe UI", "Malgun Gothic", -apple-system, BlinkMacSystemFont, sans-serif;
}

.app {
  display: flex;
  flex-direction: column;
  height: 100vh;
}

.app-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 10px 16px;
  background: var(--panel-bg);
  border-bottom: 1px solid var(--border);
}

.app-header h1 {
  font-size: 1.15rem;
  margin: 0;
}

.home-link { text-decoration: none; margin-right: 4px; }

.header-controls { display: flex; gap: 8px; }

button {
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: 6px;
  padding: 6px 14px;
  font-size: 0.85rem;
  cursor: pointer;
}
button:hover { background: var(--accent-hover); }
button.secondary {
  background: transparent;
  color: var(--text);
  border: 1px solid var(--border);
}
button.secondary:hover { background: var(--n-region); }

.app-main {
  flex: 1;
  display: flex;
  min-height: 0;
}

.stage {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: flex-start;
  padding: 16px;
  overflow: auto;
  gap: 12px;
}

#pn-canvas {
  max-width: 100%;
  height: auto;
  background: var(--panel-bg);
  border: 1px solid var(--border);
  border-radius: 10px;
}

.legend {
  display: flex;
  flex-wrap: wrap;
  gap: 12px 18px;
  font-size: 0.75rem;
  color: var(--muted);
  max-width: 960px;
}

.legend-item {
  display: flex;
  align-items: center;
  gap: 6px;
}

.dot {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  display: inline-block;
}
.dot.electron { background: var(--electron); }
.dot.electron.minor { background: var(--electron); opacity: 0.45; width: 8px; height: 8px; }
.dot.hole { background: var(--hole); }
.dot.hole.minor { background: var(--hole); opacity: 0.45; width: 8px; height: 8px; }
.dot.ion-plus, .dot.ion-minus {
  background: transparent;
  border: 1.5px solid var(--ion-plus);
}
.arrow-swatch {
  color: var(--muted);
  font-weight: bold;
}

.side-panel {
  width: 300px;
  flex: none;
  background: var(--panel-bg);
  border-left: 1px solid var(--border);
  padding: 14px;
  overflow-y: auto;
}

.side-panel h2 {
  font-size: 0.95rem;
  margin: 16px 0 8px;
}
.side-panel h2:first-child { margin-top: 0; }

.control-row {
  margin-bottom: 12px;
  font-size: 0.8rem;
}
.control-row label {
  display: block;
  margin-bottom: 4px;
  color: var(--muted);
}
.control-row input[type="range"] {
  width: 100%;
}

.bias-scale {
  display: flex;
  justify-content: space-between;
  font-size: 0.68rem;
  color: var(--muted);
}

.state-badge {
  border-radius: 6px;
  padding: 8px 10px;
  font-size: 0.8rem;
  font-weight: 600;
  text-align: center;
  margin-bottom: 14px;
}
.state-badge.equilibrium { background: var(--n-region); color: var(--text); }
.state-badge.forward { background: #22c55e33; color: #16803c; }
.state-badge.reverse { background: #ef444433; color: #b91c1c; }
@media (prefers-color-scheme: dark) {
  .state-badge.forward { color: #4ade80; }
  .state-badge.reverse { color: #fca5a5; }
}

.meter-track {
  position: relative;
  height: 18px;
  background: var(--n-region);
  border-radius: 9px;
  overflow: hidden;
  margin-bottom: 4px;
}
.meter-zero {
  position: absolute;
  left: 50%;
  top: 0;
  bottom: 0;
  width: 2px;
  background: var(--muted);
}
.meter-fill {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 50%;
  width: 0;
  background: var(--accent);
  transition: width 0.15s ease, left 0.15s ease;
}
.meter-label {
  font-size: 0.75rem;
  color: var(--muted);
  margin-bottom: 14px;
  text-align: center;
}

.info-panel {
  font-size: 0.8rem;
  line-height: 1.6;
  background: var(--n-region);
  border-radius: 6px;
  padding: 8px 10px;
  margin-bottom: 8px;
}

details {
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 6px 10px;
  margin-bottom: 12px;
}
summary {
  cursor: pointer;
  font-size: 0.85rem;
  font-weight: 600;
  padding: 4px 0;
}
.explain-panel {
  font-size: 0.78rem;
  line-height: 1.6;
  color: var(--text);
  padding-top: 6px;
}

.disclaimer {
  font-size: 0.68rem;
  color: var(--muted);
  line-height: 1.5;
}

@media (max-width: 900px) {
  .app-main { flex-direction: column; }
  .side-panel { width: 100%; border: none; border-top: 1px solid var(--border); }
}