:root {
  --bg-page:    #f4f7fa;
  --bg-panel:   #ffffff;
  --bg-cell:    #e8edf3;
  --bg-wall:    #2c3e50;
  --bg-visited: #a0d8ef;
  --bg-path:    #f3c969;
  --bg-start:   #2ecc71;
  --bg-end:     #e74c3c;
  --fg-default: #2d3436;
  --border:     #d1d8e0;
  --shadow-md:  0 4px 6px rgba(0,0,0,0.1);
  --radius:     8px;
  --gap:        4px;
  --font:       'Segoe UI', Tahoma, sans-serif;
}
* {
  box-sizing: border-box;
}
body {
  margin: 0;
  padding: 0;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  background: var(--bg-page);
  font-family: var(--font);
  color: var(--fg-default);
}
header {
  width: 100%;
  background: var(--bg-panel);
  box-shadow: var(--shadow-md);
  padding: 1rem 0;
  margin-bottom: 1.5rem;
  text-align: center;
}
header h1 {
  margin: 0;
  font-size: 2.5rem;
  font-weight: 800;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--fg-default);
  position: relative;
  display: inline-block;
}
header h1::after {
  content: '';
  display: block;
  width: 120px;
  height: 4px;
  background: var(--bg-path);
  border-radius: 2px;
  margin: 0.5rem auto 0;
}
#controls {
  display: flex;
  flex-wrap: wrap;
  gap: 20px;
  justify-content: center;
  width: min(90vw, 900px);
  margin: 24px 0;
}
.control-group {
  background: var(--bg-panel);
  box-shadow: var(--shadow-md);
  border-radius: var(--radius);
  padding: 16px;
  display: flex;
  flex-direction: column;
  gap: 12px;
  min-width: 200px;
}
.group-label {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--fg-default);
  border-bottom: 1px solid var(--border);
  padding-bottom: 4px;
  margin-bottom: 8px;
}
.primary-btn {
  width: 100%;
  max-width: 300px;
  padding: 14px 24px;
  font-size: 1.1rem;
  font-weight: 700;
  background: var(--bg-path);
  color: white;
  border: 1px solid var(--bg-path);
  border-radius: var(--radius);
  box-shadow: var(--shadow-md);
  transition: transform 0.1s, box-shadow 0.1s;
}
.primary-btn:hover:not(:disabled) {
  transform: translateY(-2px);
  box-shadow: 0 6px 10px rgba(0,0,0,0.15);
}
.primary-btn:disabled {
  opacity: 0.6;
  cursor: not-allowed;
}
.control-group button,
.control-group label input {
  width: 100%;
  padding: 8px 4px;
  font-size: 0.9rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--bg-panel);
  cursor: pointer;
  transition: background 0.2s, box-shadow 0.2s;
}
.control-group button:hover:not(:disabled) {
  background: var(--bg-cell);
  box-shadow: var(--shadow-md);
}
.control-group button:disabled {
  opacity: 0.6;
  cursor: not-allowed;
}
.control-group input[type="number"] {
  -webkit-appearance: none;
  background: var(--bg-cell);
}
.control-group label {
  display: inline-flex;
  flex-direction: row;
  align-items: center;
  gap: 8px;
  font-weight: 600;
}

.control-group input[type="range"] {
  -webkit-appearance: none;
  -moz-appearance: none;
  appearance: none;
  width: 100%;
  height: auto;
  margin: 4px 0 0;
  background: transparent;
  cursor: pointer;
}

.control-group input[type="range"]::-webkit-slider-runnable-track {
  height: auto;
  background: var(--border);
  border-radius: 6px;
}

.control-group input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  margin-top: -4px;
  width: 20px;
  height: 20px;
  background: var(--bg-path);
  border: 2px solid var(--border);
  border-radius: 50%;
  box-shadow: var(--shadow-md);
  transition: background 0.2s, transform 0.1s;
}
.control-group input[type="range"]::-webkit-slider-thumb:hover {
  background: var(--bg-start);
  transform: scale(1.1);
}

.control-group input[type="range"]::-moz-range-track {
  height: auto;
  background: var(--border);
  border-radius: 6px;
}
.control-group input[type="range"]::-moz-range-thumb {
  width: 20px;
  height: 20px;
  background: var(--bg-path);
  border: 2px solid var(--border);
  border-radius: 50%;
  box-shadow: var(--shadow-md);
  transition: background 0.2s, transform 0.1s;
}
.control-group input[type="range"]::-moz-range-thumb:hover {
  background: var(--bg-start);
  transform: scale(1.1);
}

.control-group input[type="range"]::-ms-track {
  width: 100%;
  height: auto;
  background: transparent;
  border-color: transparent;
  color: transparent;
}
.control-group input[type="range"]::-ms-fill-lower,
.control-group input[type="range"]::-ms-fill-upper {
  background: var(--border);
  border-radius: 6px;
}
.control-group input[type="range"]::-ms-thumb {
  width: 20px;
  height: 20px;
  background: var(--bg-path);
  border: 2px solid var(--border);
  border-radius: 50%;
  box-shadow: var(--shadow-md);
  transition: background 0.2s, transform 0.1s;
}
.control-group input[type="range"]::-ms-thumb:hover {
  background: var(--bg-start);
  transform: scale(1.1);
}
#main {
  display: flex;
  gap: 20px;
  align-items: flex-start;
  width: min(100vw, 1200px);
  margin-bottom: 40px;
}
.panel {
  background: var(--bg-panel);
  box-shadow: var(--shadow-md);
  border-radius: var(--radius);
  padding: 16px;
  font-size: 0.95rem;
  line-height: 1.4;
}
.instructions {
  flex: 0 0 250px;
}
.legend {
  flex: 0 0 180px;
}
.panel h2 {
  margin: 0 0 0.75rem;
  font-size: 1.25rem;
  color: var(--fg-default);
  border-bottom: 1px solid var(--border);
  padding-bottom: 8px;
}
.panel ul {
  list-style: none;
  padding: 0;
  margin: 0;
}
.instructions li,
.legend li {
  margin-bottom: 0.75rem;
  display: flex;
  align-items: center;
}
.instructions li:last-child,
.legend li:last-child {
  margin-bottom: 0;
}
.instructions li .icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 1.5em;
  font-size: 1.2rem;
  margin-right: 0.5em;
}
.legend li .cell {
  width: 1rem;
  height: 1rem;
  margin-right: 0.5rem;
  border: 1px solid var(--border);
  box-shadow: none;
}
#gridContainer {
  display: grid;
  gap: var(--gap);
  width: 600px;
  height: 600px;
  background: var(--bg-panel);
  box-shadow: var(--shadow-md);
  border-radius: var(--radius);
  overflow: hidden;
  margin-bottom: 0;
}
.cell {
  width: 100%;
  height: 100%;
  background: var(--bg-cell);
  border: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 600;
  color: var(--fg-default);
  transition: background 0.2s;
  user-select: none;
}
.cell:hover {
  background: #dbe2ec;
}
.cell.wall       { background: var(--bg-wall);       cursor: not-allowed; }
.cell.visited    { background: var(--bg-visited);    }
.cell.path       { background: var(--bg-path);       }
.cell.start      { background: var(--bg-start);      cursor: grab; }
.cell.end        { background: var(--bg-end);        cursor: grab; }
.cell.drag-over  { outline: 2px dashed var(--fg-default); }

@media (min-width: 700px) {
  .control-group.primary {
    flex: 0 0 30%;
  }
  .control-group:not(.primary) {
    flex: 0 0 30%;
  }
}
@media (max-width: 700px) {
  #gridContainer {
    width: 90vw;
    height: 90vw;
  }
}