/* ============================================================
   Base / Reset
   ============================================================ */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  /* Palette */
  --color-bg:           #0f172a;
  --color-surface:      #1e293b;
  --color-border:       #334155;
  --color-text:         #e2e8f0;
  --color-text-muted:   #94a3b8;

  /* Cell states */
  --color-cell-default: #1e293b;
  --color-cell-wall:    #0f172a;
  --color-cell-start:   #22c55e;
  --color-cell-end:     #ef4444;
  --color-cell-visited: #3b82f6;
  --color-cell-path:    #fbbf24;

  /* Sizing */
  --cell-size:  28px;
  --grid-cols:  30;
  --grid-rows:  20;
}

body {
  background-color: var(--color-bg);
  color: var(--color-text);
  font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
  height: 100vh;
  overflow: hidden;
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: 1rem 1rem 0.5rem;
}

main {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.75rem;
  width: 100%;
  max-width: 920px;
  min-height: 0;
  overflow: hidden;
}

/* ============================================================
   Utility
   ============================================================ */
.hidden { display: none !important; }

/* ============================================================
   Header
   ============================================================ */
header {
  text-align: center;
  flex-shrink: 0;
}

header h1 {
  font-size: 2rem;
  font-weight: 700;
  letter-spacing: 0.05em;
  color: var(--color-cell-path);
}

header h1 a {
  color: inherit;
  text-decoration: none;
}

header h1 a:hover {
  text-decoration: underline;
}

.subtitle {
  color: var(--color-text-muted);
  font-size: 0.95rem;
  margin-top: 0.25rem;
}

/* ============================================================
   Controls
   ============================================================ */
.controls {
  display: flex;
  align-items: flex-end;
  gap: 1rem;
  background-color: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: 0.75rem;
  padding: 0.75rem 1.25rem;
  width: 100%;
  flex-shrink: 0;
}

.control-group {
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
  flex: 1;
}

/* Legend separator — thin vertical rule between legend items and controls */
.legend-sep {
  display: inline-block;
  width: 1px;
  height: 1.1em;
  background: var(--color-border);
  margin: 0 0.25rem;
  flex-shrink: 0;
}

/* Wrapper that groups a set of legend items inline */
.legend-items {
  display: contents; /* participates in the parent flex layout inline */
}

.legend-items.hidden {
  display: none;
}

/* Speed label inside the legend */
.legend-label {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-text-muted);
}

.legend-control {
  gap: 0.4rem;
}

/* Compact button variant for inside the legend bar */
.btn-sm {
  padding: 0.3rem 0.7rem;
  font-size: 0.8rem;
}

.control-group label {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-text-muted);
}

select {
  background-color: var(--color-bg);
  color: var(--color-text);
  border: 1px solid var(--color-border);
  border-radius: 0.375rem;
  padding: 0.4rem 0.75rem;
  font-size: 0.9rem;
  cursor: pointer;
  outline: none;
  transition: border-color 0.15s;
}

select:focus {
  border-color: var(--color-cell-visited);
}

select:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

/* Buttons */
.button-group {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
  align-items: flex-end;
}

.btn {
  padding: 0.45rem 1rem;
  border: none;
  border-radius: 0.375rem;
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  transition: opacity 0.15s, transform 0.1s;
}

.btn:hover  { opacity: 0.85; }
.btn:active { transform: scale(0.97); }

.btn:disabled {
  opacity: 0.4;
  cursor: not-allowed;
  transform: none;
}

.btn-primary   { background-color: var(--color-cell-visited); color: #fff; }
.btn-secondary { background-color: var(--color-border);       color: var(--color-text); }

/* Legend — overlaid at the bottom of the visualizer tab */
.legend {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.75rem;
  align-items: center;
  padding: 0.4rem 1rem;
  background: rgba(15, 23, 42, 0.8);
  backdrop-filter: blur(4px);
  z-index: 1;
}

.legend-item {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  font-size: 0.8rem;
  color: var(--color-text-muted);
}

/* Grid legend boxes */
.legend-box {
  display: inline-block;
  width: 16px;
  height: 16px;
  border-radius: 3px;
  border: 1px solid var(--color-border);
}

.legend-box.start   { background-color: var(--color-cell-start); }
.legend-box.end     { background-color: var(--color-cell-end); }
.legend-box.wall    { background-color: var(--color-cell-wall); }
.legend-box.visited { background-color: var(--color-cell-visited); }
.legend-box.path    { background-color: var(--color-cell-path); }

/* Sampling legend swatches */
.legend-circle {
  display: inline-block;
  width: 13px;
  height: 13px;
  border-radius: 50%;
  border: 1px solid var(--color-border);
  flex-shrink: 0;
}

.legend-line {
  display: inline-block;
  width: 22px;
  height: 3px;
  border-radius: 2px;
  flex-shrink: 0;
}


/* ============================================================
   Unified panel (visualizer + algo info tabs)
   ============================================================ */
.panel {
  display: flex;
  flex-direction: column;
  flex: 1;
  min-height: 0;
  background-color: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: 0.75rem;
  padding: 0.75rem 1.25rem 0;
  width: 100%;
  overflow: hidden;
}

/* All tab panels occupy the same fixed area — no page reflow when switching */
.tab-panels {
  position: relative;
  flex: 1;
  min-height: 0;
}

.tab-content {
  position: absolute;
  inset: 0;
  overflow: auto;
  padding-bottom: 0.75rem;
}

/* Visualizer tab: canvas fills the entire panel, grid is centred */
#tab-visualizer {
  overflow: hidden;
  padding: 0;
}

.visualizer-env {
  position: absolute;
  inset: 0;
  overflow: hidden;
  display: flex;
  justify-content: center;
  align-items: flex-start;
}

/* ============================================================
   Grid
   ============================================================ */
#grid {
  display: grid;
  grid-template-columns: repeat(var(--grid-cols), var(--cell-size));
  grid-template-rows:    repeat(var(--grid-rows), var(--cell-size));
  gap: 1px;
  background-color: var(--color-border);
  border: 1px solid var(--color-border);
  user-select: none;
}

.cell {
  width: var(--cell-size);
  height: var(--cell-size);
  background-color: var(--color-cell-default);
  cursor: pointer;
  transition: background-color 0.05s;
}

.cell.wall    { background-color: var(--color-cell-wall); }
.cell.start   { background-color: var(--color-cell-start); cursor: grab; }
.cell.end     { background-color: var(--color-cell-end);   cursor: grab; }
.cell.visited { background-color: var(--color-cell-visited); animation: pop-in 0.15s ease; }
.cell.path    { background-color: var(--color-cell-path);   animation: pop-in 0.2s ease; }

@keyframes pop-in {
  0%   { transform: scale(0.6); opacity: 0.4; }
  100% { transform: scale(1);   opacity: 1; }
}

/* ============================================================
   Canvas (free-space environment)
   ============================================================ */
#canvas {
  display: block;
  width: 100%;
  height: 100%;
  align-self: stretch;
  cursor: crosshair;
  user-select: none;
}

/* ============================================================
   Algorithm info panel
   ============================================================ */
.algo-info-header {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin-bottom: 0.4rem;
  flex-wrap: wrap;
}

.algo-info-header h3 {
  font-size: 1rem;
  font-weight: 600;
  color: var(--color-text);
}

.paper-link {
  color: var(--color-cell-visited);
  font-size: 0.78rem;
  text-decoration: none;
  border: 1px solid var(--color-cell-visited);
  border-radius: 0.25rem;
  padding: 0.18rem 0.55rem;
  white-space: nowrap;
  transition: background-color 0.15s;
}

.paper-link:hover {
  background-color: rgba(59, 130, 246, 0.15);
}

.info-description {
  font-size: 0.85rem;
  color: var(--color-text-muted);
  margin-bottom: 0.75rem;
  line-height: 1.5;
}

/* Tabs */
.info-tabs {
  display: flex;
  gap: 0.25rem;
  border-bottom: 1px solid var(--color-border);
  padding-bottom: 0.5rem;
  margin-bottom: 0.5rem;
}

.tab-btn {
  background: none;
  border: 1px solid transparent;
  border-radius: 0.25rem;
  color: var(--color-text-muted);
  cursor: pointer;
  font-size: 0.8rem;
  padding: 0.25rem 0.75rem;
  transition: color 0.15s, border-color 0.15s;
}

.tab-btn:hover { color: var(--color-text); }

.tab-btn.active {
  border-color: var(--color-cell-visited);
  color: var(--color-cell-visited);
}

/* Code blocks (pseudocode / implementation) */
.code-block {
  background-color: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: 0.375rem;
  color: var(--color-text);
  font-family: 'Cascadia Code', 'Fira Code', 'Consolas', 'Courier New', monospace;
  font-size: 0.78rem;
  line-height: 1.65;
  padding: 0.75rem 1rem;
  white-space: pre;
  tab-size: 2;
  /* height is constrained by the tab-content panel; no local max-height needed */
}

/* Syntax-highlight tokens (implementation tab) */
.hl-keyword { color: #93c5fd; font-weight: 600; }  /* blue-300  */
.hl-string  { color: #86efac; }                     /* green-300 */
.hl-comment { color: #64748b; font-style: italic; } /* slate-500 */
.hl-number  { color: #fb923c; }                     /* orange-400 */
.hl-fn      { color: #fde68a; }                     /* amber-200  */

/* ============================================================
   Stats tab
   ============================================================ */
.stat-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.35rem 1.5rem;
  margin-bottom: 0.75rem;
}

.stat-row {
  display: flex;
  flex-direction: column;
  gap: 0.1rem;
}

.stat-label {
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--color-text-muted);
}

.stat-value {
  font-size: 0.85rem;
  color: var(--color-text);
}

.stat-improvement {
  grid-column: 1 / -1;
  background-color: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: 0.375rem;
  padding: 0.5rem 0.75rem;
  margin-bottom: 0.75rem;
}

.stat-improvement p {
  font-size: 0.85rem;
  color: var(--color-text);
  margin-top: 0.2rem;
  line-height: 1.45;
}

.stat-section-label {
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--color-text-muted);
  margin-bottom: 0.35rem;
  margin-top: 0.5rem;
}

.stat-badges {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
  margin-bottom: 0.25rem;
}

.stat-badge {
  font-size: 0.75rem;
  border-radius: 0.25rem;
  padding: 0.2rem 0.55rem;
  border: 1px solid transparent;
}

.stat-badge-good {
  background-color: rgba(34, 197, 94, 0.12);
  border-color: rgba(34, 197, 94, 0.35);
  color: #86efac;
}

.stat-badge-bad {
  background-color: rgba(239, 68, 68, 0.1);
  border-color: rgba(239, 68, 68, 0.3);
  color: #fca5a5;
}

/* ============================================================
   Status bar
   ============================================================ */
.status-bar {
  flex-shrink: 0;
  font-size: 0.85rem;
  color: var(--color-text-muted);
  text-align: center;
}

/* ============================================================
   Footer
   ============================================================ */
footer {
  flex-shrink: 0;
  padding-top: 0.4rem;
  font-size: 0.78rem;
  color: var(--color-text-muted);
  text-align: center;
}