:root[data-theme="light"] {
  --bg-primary: #f8fafc;
  --bg-secondary: #ffffff;
  --bg-tertiary: #f1f5f9;
  --bg-card: #e2e8f0;
  --accent-primary: #3b82f6;
  --accent-secondary: #8b5cf6;
  --accent-success: #10b981;
  --accent-warning: #f59e0b;
  --accent-error: #ef4444;
  --text-primary: #1e293b;
  --text-secondary: #475569;
  --text-muted: #64748b;
  --border-subtle: #e2e8f0;
  --border-medium: #cbd5e1;
  --glow-primary: rgba(59, 130, 246, 0.2);
  --glow-success: rgba(16, 185, 129, 0.2);
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.1);
  --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
}

/* Dark Theme */
:root[data-theme="dark"] {
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-tertiary: #334155;
  --bg-card: #475569;
  --accent-primary: #3b82f6;
  --accent-secondary: #8b5cf6;
  --accent-success: #10b981;
  --accent-warning: #f59e0b;
  --accent-error: #ef4444;
  --text-primary: #f1f5f9;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;
  --border-subtle: #334155;
  --border-medium: #475569;
  --glow-primary: rgba(59, 130, 246, 0.3);
  --glow-success: rgba(16, 185, 129, 0.3);
  --shadow-sm: 0 2px 4px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 8px rgba(0, 0, 0, 0.3);
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  height: 100vh;
  overflow: hidden;
  transition: background 0.3s ease, color 0.3s ease;
}

/* Main Layout */
.app-container {
  display: grid;
  grid-template-columns: 320px 1fr 280px;
  grid-template-rows: 60px auto 1fr 180px;
  height: 100vh;
  gap: 0;
}

/* Header */
.header {
  grid-column: 1 / -1;
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border-subtle);
  padding: 0 1.5rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  box-shadow: var(--shadow-sm);
  position: relative;
  z-index: 100;
}

.logo {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.logo-icon {
  width: 36px;
  height: 36px;
  background: linear-gradient(135deg, var(--accent-primary), var(--accent-secondary));
  border-radius: 8px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.2rem;
  box-shadow: 0 4px 12px var(--glow-primary);
  animation: float 3s ease-in-out infinite;
}

@keyframes float {
  0%, 100% { transform: translateY(0px); }
  50% { transform: translateY(-4px); }
}

.logo-text h1 {
  font-size: 1.1rem;
  font-weight: 700;
  background: linear-gradient(135deg, var(--accent-primary), var(--accent-secondary));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  letter-spacing: -0.3px;
}

.logo-text p {
  font-size: 0.7rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.header-actions {
  display: flex;
  gap: 0.75rem;
  align-items: center;
}

/* Theme Toggle */
.theme-toggle {
  width: 50px;
  height: 26px;
  background: var(--bg-tertiary);
  border: 1px solid var(--border-medium);
  border-radius: 13px;
  cursor: pointer;
  position: relative;
  transition: all 0.3s ease;
}

.theme-toggle:hover {
  border-color: var(--accent-primary);
}

.theme-toggle-slider {
  width: 20px;
  height: 20px;
  background: var(--accent-primary);
  border-radius: 50%;
  position: absolute;
  top: 2px;
  left: 3px;
  transition: transform 0.3s ease;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.7rem;
  box-shadow: var(--shadow-sm);
}

:root[data-theme="dark"] .theme-toggle-slider {
  transform: translateX(24px);
}

.header-btn {
  padding: 0.5rem 1rem;
  background: var(--bg-tertiary);
  border: 1px solid var(--border-medium);
  border-radius: 6px;
  color: var(--text-secondary);
  font-size: 0.8rem;
  cursor: pointer;
  transition: all 0.2s ease;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.header-btn:hover {
  border-color: var(--accent-primary);
  color: var(--accent-primary);
  transform: translateY(-1px);
}

.kbd-hint {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.4rem 0.75rem;
  background: var(--bg-tertiary);
  border: 1px solid var(--border-subtle);
  border-radius: 6px;
  font-size: 0.7rem;
  color: var(--text-muted);
}

.kbd {
  padding: 0.2rem 0.4rem;
  background: var(--bg-primary);
  border: 1px solid var(--border-subtle);
  border-radius: 3px;
  font-family: monospace;
  font-size: 0.65rem;
  color: var(--accent-primary);
  min-width: 18px;
  text-align: center;
}

/* Metrics Banner */
.metrics-banner {
  grid-column: 2 / 3;
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border-subtle);
  border-left: 1px solid var(--border-subtle);
  border-right: 1px solid var(--border-subtle);
  padding: 0.75rem 1.5rem;
  display: flex;
  gap: 1.5rem;
  align-items: center;
}

.metric {
  flex: 1;
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.6rem 1rem;
  background: var(--bg-tertiary);
  border-radius: 8px;
  border: 1px solid var(--border-medium);
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  position: relative;
  overflow: hidden;
}

.metric::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  width: 3px;
  height: 100%;
  background: var(--accent-primary);
  transform: scaleY(0);
  transition: transform 0.3s ease;
}

.metric:hover::before {
  transform: scaleY(1);
}

.metric:hover {
  border-color: var(--accent-primary);
  box-shadow: 0 4px 12px var(--glow-primary);
}

.metric-icon {
  font-size: 1.4rem;
  opacity: 0.8;
}

.metric-content {
  display: flex;
  flex-direction: column;
  gap: 0.1rem;
}

.metric-label {
  font-size: 0.65rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  font-weight: 600;
}

.metric-value {
  font-size: 1.3rem;
  font-weight: 700;
  font-family: 'Courier New', monospace;
  color: var(--accent-primary);
}

/* Left Panel - Input Controls */
.left-panel {
  grid-column: 1;
  grid-row: 2 / -1;
  background: var(--bg-secondary);
  border-right: 1px solid var(--border-subtle);
  overflow-y: auto;
  overflow-x: hidden;
}

.panel-section {
  padding: 1.25rem;
  border-bottom: 1px solid var(--border-subtle);
}

.section-title {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin-bottom: 1rem;
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-primary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.section-icon {
  font-size: 0.9rem;
  color: var(--accent-primary);
}

/* Preset Buttons */
.preset-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 0.5rem;
  margin-bottom: 0.75rem;
}

.preset-btn {
  background: var(--bg-tertiary);
  border: 1px solid var(--border-medium);
  color: var(--text-secondary);
  padding: 0.7rem 0.5rem;
  border-radius: 6px;
  font-size: 0.75rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s ease;
  position: relative;
  overflow: hidden;
}

.preset-btn::after {
  content: '';
  position: absolute;
  top: 50%;
  left: 50%;
  width: 0;
  height: 0;
  border-radius: 50%;
  background: var(--glow-primary);
  transform: translate(-50%, -50%);
  transition: width 0.4s ease, height 0.4s ease;
}

.preset-btn:hover::after {
  width: 150px;
  height: 150px;
}

.preset-btn:hover {
  border-color: var(--accent-primary);
  color: var(--accent-primary);
  transform: translateY(-2px);
}

.preset-btn.active {
  background: var(--glow-primary);
  border-color: var(--accent-primary);
  color: var(--accent-primary);
}

/* Random Generator */
.random-section {
  margin-top: 0.75rem;
}

.random-btn {
  width: 100%;
  padding: 0.85rem;
  background: linear-gradient(135deg, var(--accent-secondary), var(--accent-primary));
  border: none;
  border-radius: 6px;
  color: white;
  font-size: 0.8rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.3s ease;
  box-shadow: 0 4px 12px rgba(139, 92, 246, 0.3);
  position: relative;
  overflow: hidden;
}

.random-btn::before {
  content: '🎲';
  position: absolute;
  font-size: 3rem;
  opacity: 0.1;
  right: -10px;
  top: 50%;
  transform: translateY(-50%) rotate(20deg);
  transition: all 0.3s ease;
}

.random-btn:hover::before {
  transform: translateY(-50%) rotate(0deg) scale(1.2);
}

.random-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(139, 92, 246, 0.4);
}

.random-controls {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.5rem;
  margin-top: 0.75rem;
}

.input-group {
  margin-bottom: 0;
}

.input-label {
  display: block;
  font-size: 0.7rem;
  color: var(--text-secondary);
  margin-bottom: 0.4rem;
  font-weight: 500;
}

.input-field {
  width: 100%;
  padding: 0.6rem;
  background: var(--bg-primary);
  border: 1px solid var(--border-medium);
  border-radius: 6px;
  color: var(--text-primary);
  font-size: 0.75rem;
  transition: all 0.2s ease;
}

.input-field:focus {
  outline: none;
  border-color: var(--accent-primary);
  box-shadow: 0 0 0 3px var(--glow-primary);
}

/* Input Methods Tabs */
.input-tabs {
  display: flex;
  gap: 0.5rem;
  margin-bottom: 0.75rem;
}

.input-tab {
  flex: 1;
  padding: 0.5rem;
  background: var(--bg-tertiary);
  border: 1px solid var(--border-medium);
  border-radius: 6px;
  font-size: 0.7rem;
  font-weight: 600;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all 0.2s ease;
  text-align: center;
}

.input-tab:hover {
  border-color: var(--accent-primary);
  color: var(--accent-primary);
}

.input-tab.active {
  background: var(--glow-primary);
  border-color: var(--accent-primary);
  color: var(--accent-primary);
}

.input-content {
  display: none;
}

.input-content.active {
  display: block;
}

textarea.input-field {
  font-family: 'Courier New', monospace;
  resize: vertical;
  min-height: 100px;
}

.input-hint {
  font-size: 0.65rem;
  color: var(--text-muted);
  margin-top: 0.4rem;
  font-style: italic;
}

/* Control Buttons */
.control-buttons {
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.control-btn {
  width: 100%;
  padding: 0.8rem;
  border: none;
  border-radius: 6px;
  font-size: 0.8rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s ease;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  position: relative;
  overflow: hidden;
}

.control-btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.btn-primary {
  background: linear-gradient(135deg, var(--accent-primary), var(--accent-secondary));
  color: white;
  box-shadow: 0 4px 12px var(--glow-primary);
}

.btn-primary:hover:not(:disabled) {
  transform: translateY(-2px);
  box-shadow: 0 6px 16px var(--glow-primary);
}

.btn-secondary {
  background: var(--bg-tertiary);
  color: var(--text-secondary);
  border: 1px solid var(--border-medium);
}

.btn-secondary:hover:not(:disabled) {
  border-color: var(--accent-primary);
  color: var(--accent-primary);
}

.btn-danger {
  background: var(--accent-error);
  color: white;
}

.btn-danger:hover:not(:disabled) {
  background: #dc2626;
  transform: translateY(-2px);
}

/* Canvas Container */
.canvas-container {
  grid-column: 2;
  grid-row: 3;
  background: var(--bg-secondary);
  border-left: 1px solid var(--border-subtle);
  border-right: 1px solid var(--border-subtle);
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

/* Canvas Controls — single fixed-height bar, never overlaps SVG */
.canvas-controls {
  flex-shrink: 0;
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.4rem 0.75rem;
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border-subtle);
  z-index: 50;
  flex-wrap: nowrap;
  overflow: hidden;
}

.canvas-btn {
  padding: 0.5rem 0.9rem;
  background: var(--bg-tertiary);
  border: 1px solid var(--border-medium);
  border-radius: 6px;
  color: var(--text-secondary);
  font-size: 0.75rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s ease;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex-shrink: 0;
  white-space: nowrap;
}

.canvas-btn:hover {
  border-color: var(--accent-primary);
  color: var(--accent-primary);
  transform: translateY(-1px);
}

.canvas-btn.active {
  background: var(--glow-primary);
  border-color: var(--accent-primary);
  color: var(--accent-primary);
}

#canvas {
  flex: 1;
  width: 100%;
  display: block;
  min-height: 0;
}

/* Right Panel - Algorithm Status */
.right-panel {
  grid-column: 3;
  grid-row: 2 / -1;
  background: var(--bg-secondary);
  border-left: 1px solid var(--border-subtle);
  overflow-y: auto;
  overflow-x: hidden;
}

/* Algorithm Steps */
.algorithm-steps {
  padding: 1rem;
}

.step {
  padding: 0.85rem;
  background: var(--bg-tertiary);
  border-left: 3px solid var(--border-medium);
  border-radius: 6px;
  margin-bottom: 0.6rem;
  transition: all 0.3s ease;
  cursor: pointer;
}

.step:hover {
  border-left-color: var(--accent-primary);
  transform: translateX(4px);
}

.step.active {
  background: var(--glow-primary);
  border-left-color: var(--accent-primary);
  box-shadow: 0 4px 12px var(--glow-primary);
}

.step-header {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  margin-bottom: 0.4rem;
}

.step-number {
  width: 24px;
  height: 24px;
  background: var(--bg-primary);
  border: 2px solid var(--border-medium);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.7rem;
  font-weight: 700;
  color: var(--text-secondary);
  transition: all 0.3s ease;
}

.step.active .step-number {
  background: var(--accent-primary);
  border-color: var(--accent-primary);
  color: white;
  animation: pulse 2s infinite;
}

@keyframes pulse {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.1); }
}

.step-title {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-primary);
}

.step-desc {
  font-size: 0.7rem;
  color: var(--text-secondary);
  line-height: 1.5;
}

/* Execution Log */
.execution-log {
  padding: 1rem;
  max-height: 250px;
  overflow-y: auto;
}

.log-entry {
  display: flex;
  gap: 0.6rem;
  padding: 0.5rem;
  font-size: 0.7rem;
  font-family: 'Courier New', monospace;
  border-bottom: 1px solid var(--border-subtle);
  transition: background 0.2s ease;
}

.log-entry:hover {
  background: var(--bg-tertiary);
}

.log-time {
  color: var(--text-muted);
  font-size: 0.65rem;
  min-width: 45px;
}

.log-message {
  color: var(--text-secondary);
  flex: 1;
}

.log-entry.success .log-message { color: var(--accent-success); }
.log-entry.error .log-message { color: var(--accent-error); }
.log-entry.warning .log-message { color: var(--accent-warning); }
.log-entry.info .log-message { color: var(--accent-info); }

/* Path History Timeline (Below Canvas) */
.path-history-container {
  grid-column: 2;
  grid-row: 4;
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-subtle);
  border-left: 1px solid var(--border-subtle);
  border-right: 1px solid var(--border-subtle);
  padding: 1rem 1.5rem;
  overflow-x: auto;
  overflow-y: hidden;
}

.path-history-header {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin-bottom: 0.75rem;
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--text-primary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.path-timeline {
  display: flex;
  gap: 1rem;
  min-height: 80px;
  align-items: center;
}

.path-card {
  min-width: 250px;
  padding: 0.85rem 1rem;
  background: var(--bg-tertiary);
  border: 1px solid var(--border-medium);
  border-radius: 8px;
  transition: all 0.3s ease;
  position: relative;
  animation: slideIn 0.4s ease;
}

@keyframes slideIn {
  from {
    opacity: 0;
    transform: translateX(-20px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

.path-card:hover {
  border-color: var(--accent-primary);
  transform: translateY(-2px);
  box-shadow: 0 4px 12px var(--glow-primary);
}

.path-card::before {
  content: attr(data-path-number);
  position: absolute;
  top: -8px;
  left: 10px;
  padding: 0.2rem 0.5rem;
  background: var(--accent-primary);
  color: white;
  font-size: 0.65rem;
  font-weight: 700;
  border-radius: 4px;
}

.path-nodes {
  font-family: 'Courier New', monospace;
  font-size: 0.8rem;
  color: var(--text-primary);
  font-weight: 600;
  margin-bottom: 0.5rem;
}

.path-info {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.7rem;
}

.path-bottleneck {
  color: var(--accent-warning);
}

.path-flow {
  padding: 0.2rem 0.6rem;
  background: var(--glow-success);
  color: var(--accent-success);
  border-radius: 4px;
  font-weight: 600;
}

.path-placeholder {
  width: 100%;
  height: 80px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  color: var(--text-muted);
  font-size: 0.75rem;
}

.path-placeholder-icon {
  font-size: 2rem;
  margin-bottom: 0.5rem;
  opacity: 0.3;
}

/* Scrollbar Styling */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

::-webkit-scrollbar-track {
  background: var(--bg-primary);
}

::-webkit-scrollbar-thumb {
  background: var(--border-medium);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--border-subtle);
}

/* Toast Notifications */
.toast {
  position: fixed;
  top: 80px;
  right: 20px;
  padding: 1rem 1.25rem;
  background: var(--bg-tertiary);
  border: 1px solid var(--border-medium);
  border-radius: 8px;
  box-shadow: var(--shadow-md);
  display: flex;
  align-items: center;
  gap: 0.75rem;
  z-index: 1000;
  animation: toastIn 0.3s ease;
  font-size: 0.8rem;
}

@keyframes toastIn {
  from {
    opacity: 0;
    transform: translateX(100%);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

.toast.success { border-left: 4px solid var(--accent-success); }
.toast.error { border-left: 4px solid var(--accent-error); }
.toast.warning { border-left: 4px solid var(--accent-warning); }
.toast.info { border-left: 4px solid var(--accent-info); }

.toast-icon {
  font-size: 1.2rem;
}

.toast.success .toast-icon { color: var(--accent-success); }
.toast.error .toast-icon { color: var(--accent-error); }
.toast.warning .toast-icon { color: var(--accent-warning); }
.toast.info .toast-icon { color: var(--accent-info); }

/* SVG Node Styling */
.node {
  cursor: pointer;
  transition: all 0.3s ease;
}

.node:hover .node-circle {
  filter: brightness(1.1);
  stroke-width: 3;
}

.node-circle {
  transition: all 0.3s ease;
}

.node.source .node-circle {
  fill: var(--accent-success);
  stroke: #059669;
}

.node.sink .node-circle {
  fill: var(--accent-error);
  stroke: #dc2626;
}

.node.visited .node-circle {
  fill: var(--accent-warning);
  stroke: #f59e0b;
}

/* Subtle path animation with green heartbeat ripple */
.edge {
  transition: all 0.3s ease;
}
.edge.path {
  stroke: var(--accent-success);
  stroke-width: 3;
}

.edge.path path {
  animation: pathPulse 1.5s ease-in-out infinite;
}

@keyframes pathPulse {
  0%, 100% { 
    filter: drop-shadow(0 0 2px rgba(16, 185, 129, 0.3));
  }
  50% { 
    filter: drop-shadow(0 0 6px rgba(16, 185, 129, 0.6));
  }
}

.edge.saturated {
  stroke: var(--text-muted);
  stroke-dasharray: 5, 5;
  opacity: 0.4;
}

/* Tooltip */
.tooltip {
  position: fixed;
  padding: 0.5rem 0.75rem;
  background: var(--bg-tertiary);
  border: 1px solid var(--border-medium);
  border-radius: 6px;
  font-size: 0.7rem;
  color: var(--text-primary);
  pointer-events: none;
  z-index: 1000;
  opacity: 0;
  transition: opacity 0.2s ease;
  box-shadow: var(--shadow-md);
}

.tooltip.show {
  opacity: 1;
}

/* Responsive adjustments */
@media (max-width: 1400px) {
  .app-container {
    grid-template-columns: 280px 1fr 260px;
  }
}

/* ============================================
   MOBILE LAYOUT — phones only (≤ 768px)
   Desktop grid is completely untouched above.
   ============================================ */
@media (max-width: 768px) {

  /* Allow page to scroll vertically on mobile */
  body {
    height: auto;
    overflow: auto;
    overflow-x: hidden;
  }

  /* Stack everything vertically */
  .app-container {
    display: flex;
    flex-direction: column;
    height: auto;
    min-height: 100vh;
  }

  /* Header: compress on mobile */
  .header {
    padding: 0 1rem;
    flex-wrap: wrap;
    gap: 0.5rem;
    min-height: 56px;
    height: auto;
    padding-top: 0.5rem;
    padding-bottom: 0.5rem;
  }

  /* Hide keyboard hints on mobile — not useful on touch */
  .kbd-hint {
    display: none;
  }

  .logo-text h1 {
    font-size: 0.95rem;
  }

  /* Metrics banner: 2x2 grid on mobile */
  .metrics-banner {
    order: 0;
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 0.5rem;
    padding: 0.75rem;
    border-left: none;
    border-right: none;
  }

  .metric {
    padding: 0.5rem 0.75rem;
  }

  .metric-icon {
    font-size: 1.1rem;
  }

  .metric-value {
    font-size: 1rem;
  }

  /* Left panel (inputs) goes on top */
  .left-panel {
    order: 1;
    grid-column: unset;
    grid-row: unset;
    width: 100%;
    overflow: visible;
    border-right: none;
    border-bottom: 1px solid var(--border-subtle);
  }

  /* Canvas section in the middle */
  .canvas-container {
    order: 2;
    grid-column: unset;
    grid-row: unset;
    width: 100%;
    /* Fixed height so the SVG renders properly */
    height: 70vw;
    min-height: 300px;
    max-height: 480px;
    border-left: none;
    border-right: none;
    border-top: 1px solid var(--border-subtle);
    border-bottom: 1px solid var(--border-subtle);
    /* Scroll target anchor */
    scroll-margin-top: 8px;
  }

  /* Path timeline below canvas */
  .path-history-container {
    order: 3;
    grid-column: unset;
    grid-row: unset;
    width: 100%;
    border-left: none;
    border-right: none;
    overflow-x: auto;
  }

  /* Right panel (algorithm steps + log) at the bottom */
  .right-panel {
    order: 4;
    grid-column: unset;
    grid-row: unset;
    width: 100%;
    overflow: visible;
    border-left: none;
    border-top: 1px solid var(--border-subtle);
  }

  /* Make algorithm steps horizontal scrollable strip on mobile */
  .algorithm-steps {
    display: flex;
    flex-direction: row;
    overflow-x: auto;
    gap: 0.5rem;
    padding: 0.75rem;
    padding-bottom: 1rem;
    -webkit-overflow-scrolling: touch;
  }

  .step {
    min-width: 130px;
    flex-shrink: 0;
    margin-bottom: 0;
  }

  /* Control buttons: 2-column grid on mobile */
  .control-buttons {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 0.5rem;
  }

  /* Make preset grid 4 across on wide phones, 2 on narrow */
  .preset-grid {
    grid-template-columns: repeat(4, 1fr);
  }

  @media (max-width: 420px) {
    .preset-grid {
      grid-template-columns: repeat(2, 1fr);
    }
  }

  /* Execution log: limit height on mobile */
  .execution-log {
    max-height: 160px;
  }
}

/* ============================================
   RESIDUAL VIEW — backward edge styling
   ============================================ */

/* Backward residual edge (added via JS) */
.edge.backward-residual path {
  stroke-dasharray: 6 3;
  opacity: 0.75;
}

.edge.backward-residual {
  pointer-events: none;
}

/* Residual view legend — inline next to the toggle button */
.residual-info-panel {
  display: none;
  align-items: center;
  gap: 1rem;
  font-size: 0.7rem;
  color: var(--text-secondary);
  border-left: 1px solid var(--border-subtle);
  padding-left: 0.75rem;
  overflow: hidden;
  flex-shrink: 1;
  min-width: 0;
}

.residual-info-panel.visible {
  display: flex;
}

.residual-legend-item {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  white-space: nowrap;
}

.residual-legend-line {
  width: 28px;
  height: 2px;
  border-radius: 2px;
  flex-shrink: 0;
}

.residual-legend-line.forward {
  background: var(--accent-primary);
}

.residual-legend-line.backward {
  background: var(--accent-warning);
  background: repeating-linear-gradient(
    90deg,
    var(--accent-warning) 0px,
    var(--accent-warning) 4px,
    transparent 4px,
    transparent 7px
  );
  height: 2px;
}

.residual-legend-line.zero {
  background: var(--text-muted);
  opacity: 0.4;
}