:root {
  --bg: #f4f6f9;
  --panel-bg: #ffffff;
  --border: #d7dce3;
  --text: #1c2430;
  --muted: #6b7684;
  --accent: #2563eb;
  --accent-hover: #1d4ed8;
  --wire: #334155;
  --electron: #2563eb;
  --conducting: #16a34a;
  --blocking: #dc2626;
  --current-arrow: #f59e0b;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #12161c;
    --panel-bg: #1a2029;
    --border: #2b3340;
    --text: #e6eaf0;
    --muted: #93a0b0;
    --accent: #4d8dff;
    --accent-hover: #6ea0ff;
    --wire: #b7c1cd;
    --electron: #5b9dff;
    --conducting: #4ade80;
    --blocking: #f87171;
    --current-arrow: #fbbf24;
  }
}

* { 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);
  flex-wrap: wrap;
}

.app-header h1 { font-size: 1.15rem; margin: 0; }
.home-link { text-decoration: none; margin-right: 4px; }

.mode-tabs { display: flex; gap: 6px; }
.tab {
  background: transparent;
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 6px 14px;
  font-size: 0.85rem;
  cursor: pointer;
}
.tab.active { background: var(--accent); color: #fff; border-color: var(--accent); }

button {
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: 6px;
  padding: 6px 12px;
  font-size: 0.85rem;
  cursor: pointer;
}
button:hover { background: var(--accent-hover); }

.btn-toggle { display: flex; gap: 6px; }
.btn-toggle button {
  flex: 1;
  background: transparent;
  color: var(--text);
  border: 1px solid var(--border);
  font-size: 0.78rem;
  padding: 6px 4px;
}
.btn-toggle button.active { background: var(--accent); color: #fff; border-color: var(--accent); }

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

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

#circuit-svg {
  width: 100%;
  max-width: 700px;
  height: auto;
  background: var(--panel-bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  color: var(--wire);
}

.wire { stroke: var(--wire); stroke-width: 2.5; fill: none; }
.comp-line { stroke: var(--wire); stroke-width: 2.5; fill: none; }
.node-dot { fill: var(--wire); }
.value-label { fill: var(--muted); font-size: 12px; }
.state-label { font-size: 11px; font-weight: 700; }
.state-label.conducting { fill: var(--conducting); }
.state-label.blocking { fill: var(--blocking); }
.diode-shape.conducting { stroke: var(--conducting); fill: none; }
.diode-shape.blocking { stroke: var(--blocking); fill: none; }
.current-arrow { fill: var(--current-arrow); }

.legend {
  display: flex;
  flex-wrap: wrap;
  gap: 10px 18px;
  font-size: 0.75rem;
  color: var(--muted);
  max-width: 700px;
}
.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.conducting { background: var(--conducting); }
.dot.blocking { background: var(--blocking); }
.arrow-swatch { color: var(--current-arrow); font-weight: bold; }
.arrow-swatch.orange { color: var(--current-arrow); }

.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%; }

.info-panel {
  font-size: 0.8rem;
  line-height: 1.7;
  background: color-mix(in srgb, var(--accent) 10%, var(--panel-bg));
  border-radius: 6px;
  padding: 8px 10px;
  margin-bottom: 8px;
}

.explain-panel {
  font-size: 0.78rem;
  line-height: 1.6;
  color: var(--text);
  margin-bottom: 10px;
}

.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); }
}