:root {
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-card: #1e293b;
  --bg-hover: #334155;
  --text-primary: #f1f5f9;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;
  --accent-blue: #3b82f6;
  --accent-red: #ef4444;
  --accent-green: #10b981;
  --accent-yellow: #f59e0b;
  --accent-purple: #8b5cf6;
  --accent-cyan: #06b6d4;
  --border-color: #334155;
}

* { margin: 0; padding: 0; box-sizing: border-box; }

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  min-height: 100vh;
  line-height: 1.6;
}

.filter-container { max-width: 1500px; margin: 0 auto; padding: 20px; }

header { text-align: center; margin-bottom: 24px; }
header h1 {
  font-size: 1.8rem; font-weight: 700;
  background: linear-gradient(135deg, var(--accent-blue), var(--accent-cyan));
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
  margin-bottom: 6px;
}
header .subtitle { color: var(--text-secondary); font-size: 0.95rem; }

.main-layout { display: grid; grid-template-columns: 1fr 300px; gap: 20px; }

@media (max-width: 1024px) {
  .main-layout { grid-template-columns: 1fr; }
}

/* Canvas grid - 2x2 */
.canvas-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
}

@media (max-width: 768px) {
  .canvas-grid { grid-template-columns: 1fr; }
}

.canvas-section {
  background: var(--bg-card);
  border-radius: 12px;
  border: 1px solid var(--border-color);
  overflow: hidden;
}

.canvas-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 8px 14px;
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--text-secondary);
  background: rgba(0,0,0,0.2);
  border-bottom: 1px solid var(--border-color);
}

.canvas-hint {
  font-size: 0.7rem;
  font-weight: 400;
  color: var(--text-muted);
}

.canvas-wrapper {
  position: relative;
  width: 100%;
  aspect-ratio: 4 / 3;
  min-height: 280px;
}

.canvas-wrapper canvas {
  width: 100%; height: 100%; display: block;
  cursor: default;
}

/* Controls Panel */
.controls-panel {
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.control-card {
  background: var(--bg-card);
  border-radius: 12px;
  border: 1px solid var(--border-color);
  padding: 14px;
}

.control-card h3 {
  font-size: 0.82rem; font-weight: 600; color: var(--text-secondary);
  text-transform: uppercase; letter-spacing: 0.05em; margin-bottom: 10px;
}

.preset-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 6px;
}

.preset-btn {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: 8px;
  padding: 8px 6px;
  color: var(--text-primary);
  font-size: 0.78rem;
  cursor: pointer;
  transition: all 0.2s;
  text-align: center;
}

.preset-btn:hover { background: var(--bg-hover); border-color: var(--accent-blue); }
.preset-btn.active { background: rgba(59,130,246,0.15); border-color: var(--accent-blue); color: var(--accent-blue); }

.preset-btn .preset-name { display: block; font-weight: 600; }

.slider-group { margin-bottom: 12px; }
.slider-group:last-child { margin-bottom: 0; }

.slider-label {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.78rem;
  color: var(--text-secondary);
  margin-bottom: 5px;
}

.slider-value { font-weight: 600; color: var(--text-primary); min-width: 50px; text-align: right; font-size: 0.75rem; }

input[type="range"] {
  width: 100%; height: 6px;
  -webkit-appearance: none; appearance: none;
  background: var(--bg-primary); border-radius: 3px; outline: none;
}

input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  width: 16px; height: 16px; border-radius: 50%;
  background: var(--accent-blue); cursor: pointer;
  transition: transform 0.15s;
}

input[type="range"]::-webkit-slider-thumb:hover { transform: scale(1.2); }

input[type="range"]::-moz-range-thumb {
  width: 16px; height: 16px; border-radius: 50%;
  background: var(--accent-blue); cursor: pointer; border: none;
}

select {
  width: 100%;
  padding: 7px 10px;
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: 8px;
  color: var(--text-primary);
  font-size: 0.8rem;
  outline: none;
  cursor: pointer;
}

select:focus { border-color: var(--accent-blue); }

.toggle-btn {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: 6px;
  padding: 3px 10px;
  color: var(--text-secondary);
  font-size: 0.7rem;
  cursor: pointer;
  transition: all 0.2s;
}

.toggle-btn:hover { border-color: var(--accent-blue); color: var(--accent-blue); }
.toggle-btn.active { background: rgba(59,130,246,0.15); border-color: var(--accent-blue); color: var(--accent-blue); }

.checkbox-label {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.8rem;
  color: var(--text-secondary);
  cursor: pointer;
  margin-bottom: 8px;
}

.checkbox-label input[type="checkbox"] {
  width: 16px; height: 16px;
  accent-color: var(--accent-blue);
  cursor: pointer;
}

.hint-text {
  font-size: 0.7rem;
  color: var(--text-muted);
  line-height: 1.5;
}

/* Stats */
.stats-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 6px;
}

.stat-item {
  background: var(--bg-primary);
  border-radius: 8px;
  padding: 8px;
  text-align: center;
}

.stat-item.full-width { grid-column: 1 / -1; }

.stat-label { font-size: 0.65rem; color: var(--text-muted); margin-bottom: 2px; }
.stat-value { font-size: 0.95rem; font-weight: 700; color: var(--text-primary); }
.stat-value.stable { color: var(--accent-green); }
.stat-value.unstable { color: var(--accent-red); }

.reset-btn {
  width: 100%; padding: 10px;
  background: var(--bg-primary); border: 1px solid var(--border-color);
  border-radius: 8px; color: var(--text-secondary);
  font-size: 0.85rem; cursor: pointer; transition: all 0.2s;
}

.reset-btn:hover { background: var(--bg-hover); color: var(--text-primary); }

/* Explanation */
.explanation {
  background: var(--bg-card);
  border-radius: 12px;
  border: 1px solid var(--border-color);
  padding: 24px;
  margin-top: 20px;
}

.explanation h2 { font-size: 1.1rem; margin-bottom: 16px; color: var(--text-primary); }
.explanation p { color: var(--text-secondary); font-size: 0.9rem; margin-bottom: 12px; line-height: 1.7; }
.explanation p:last-child { margin-bottom: 0; }

/* Legend bar */
.legend-bar {
  display: flex; flex-wrap: wrap; gap: 16px; padding: 10px 16px;
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-color);
  border-radius: 0 0 12px 12px;
  font-size: 0.78rem; color: var(--text-secondary);
}
.legend-item { display: flex; align-items: center; gap: 6px; }
.legend-swatch { width: 16px; height: 3px; border-radius: 2px; }
.legend-swatch.zero-swatch { background: var(--accent-blue); }
.legend-swatch.pole-swatch { background: var(--accent-red); }
.legend-swatch.unit-swatch { background: var(--accent-green); border-style: dashed; border-width: 1px; height: 0; }
.legend-swatch.minus3db-swatch { background: var(--accent-yellow); border-style: dashed; border-width: 1px; height: 0; }

@media (max-width: 768px) {
  .filter-container { padding: 12px; }
  header h1 { font-size: 1.4rem; }
  .canvas-wrapper { aspect-ratio: 1 / 1; min-height: 260px; }
  .canvas-grid { gap: 10px; }
  .legend-bar { gap: 10px; font-size: 0.7rem; }
}