:root {
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --accent-primary: #6366f1; /* Indigo for Hanoi */
  --text-primary: #f1f5f9;
  --text-secondary: #94a3b8;
  --border-color: rgba(255, 255, 255, 0.1);
  --rod-color: #475569;
  --disk-1: #f87171;
  --disk-2: #fb923c;
  --disk-3: #fbbf24;
  --disk-4: #4ade80;
  --disk-5: #22d3ee;
  --disk-6: #818cf8;
  --disk-7: #c084fc;
}

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

body {
  background: var(--bg-primary);
  color: var(--text-primary);
  font-family: "Inter", sans-serif;
  overflow-x: hidden;
  overflow-y: auto;
  min-height: 100vh;
}

.top-nav {
  height: 60px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0 2rem;
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border-color);
}

.nav-brand {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--accent-primary);
  text-decoration: none;
}

.simulator-container {
    display: grid;
    grid-template-columns: 280px 1fr 350px;
    height: calc(100vh - 60px);
    overflow: hidden;
}

@media (max-width: 1200px) {
  .simulator-container {
    grid-template-columns: 250px 1fr;
  }
  .explanation-side {
    grid-column: span 2;
    border-left: none;
    border-top: 1px solid var(--border-color);
  }
}

@media (max-width: 850px) {
  .simulator-container {
    grid-template-columns: 1fr;
  }
  .sidebar {
    border-right: none;
    border-bottom: 1px solid var(--border-color);
  }
  .explanation-side {
    grid-column: span 1;
  }
}

/* Sidebar */
.sidebar {
  background: var(--bg-secondary);
  border-right: 1px solid var(--border-color);
  padding: 1.5rem;
  display: flex;
  flex-direction: column;
}
.sidebar h2 {
  font-size: 0.8rem;
  color: var(--text-secondary);
  text-transform: uppercase;
  margin-bottom: 1.5rem;
}

.disk-selector {
  display: flex;
  gap: 0.5rem;
  margin-top: 0.5rem;
}
.disk-btn {
  flex: 1;
  padding: 0.5rem;
  background: rgba(255, 255, 255, 0.05);
  border: 1px solid var(--border-color);
  border-radius: 6px;
  color: var(--text-primary);
  cursor: pointer;
  transition: all 0.2s;
}
.disk-btn.active {
  background: var(--accent-primary);
  border-color: var(--accent-primary);
}

.disk-input-container {
  display: flex;
  gap: 0.5rem;
  margin-top: 0.5rem;
}
#disk-input {
  flex: 1;
  background: #0f172a;
  border: 1px solid var(--border-color);
  border-radius: 6px;
  color: white;
  padding: 0.5rem;
  font-size: 0.9rem;
}
.primary-btn {
  background: var(--accent-primary);
  border: none;
  color: white;
  padding: 0.5rem 1rem;
  border-radius: 6px;
  font-weight: 600;
  cursor: pointer;
}

.controls-panel {
  margin-top: 2rem;
}
.controls-panel h3 {
  font-size: 0.75rem;
  color: var(--text-secondary);
  margin-bottom: 1rem;
}

.main-controls {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 1rem;
  margin: 1rem 0;
}
.play-btn {
  width: 45px;
  height: 45px;
  border-radius: 50%;
  background: var(--accent-primary);
  border: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
}
.icon-btn {
  background: none;
  border: none;
  color: white;
  font-size: 1.2rem;
  cursor: pointer;
  opacity: 0.8;
}

.secondary-btn {
  width: 100%;
  padding: 0.75rem;
  background: rgba(255, 255, 255, 0.05);
  border: 1px solid var(--border-color);
  border-radius: 6px;
  color: white;
  cursor: pointer;
  margin-top: 1rem;
}

/* Visualizer Area */
.visualizer-area { 
    padding: 1.5rem; 
    display: flex; 
    flex-direction: column; 
    background: #0c1220; 
    height: 100%;
    overflow: hidden;
}
.viz-header {
  display: flex;
  justify-content: space-between;
  margin-bottom: 2rem;
}
.legend-item {
  font-size: 0.75rem;
  color: var(--text-secondary);
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin-left: 1rem;
}
.dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
}
.dot.source {
  background: var(--disk-1);
}
.dot.aux {
  background: var(--disk-4);
}
.dot.target {
  background: var(--disk-7);
}

.hanoi-workspace {
  flex: 3;
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
  width: 100%;
  background: rgba(255,255,255,0.02);
  border-radius: 12px;
  margin-bottom: 1rem;
}

.rods-container { 
    display: flex; 
    width: 100%; 
    justify-content: center; 
    gap: 3rem;
    align-items: flex-end; 
    height: 280px; 
    padding: 0 10px;
    max-width: 900px;
}

.rod {
  position: relative;
  width: 180px;
  height: 100%;
  display: flex;
  flex-direction: column-reverse;
  align-items: center;
}

.rod-base {
  width: 90%;
  height: 14px;
  background: linear-gradient(to bottom, #64748b, #334155);
  border-radius: 7px;
  z-index: 5;
  box-shadow: 0 4px 8px rgba(0,0,0,0.6);
  border: 1px solid rgba(255,255,255,0.1);
}

.rod-stem {
  width: 12px;
  height: 220px;
  background: linear-gradient(to right, #94a3b8, #cbd5e1, #94a3b8);
  border-radius: 6px;
  position: absolute;
  bottom: 14px;
  left: 50%;
  transform: translateX(-50%);
  z-index: 2;
  box-shadow: 2px 0 10px rgba(0,0,0,0.5);
  border: 1px solid rgba(255,255,255,0.05);
}

.rod-label {
  position: absolute;
  bottom: -25px;
  font-size: 0.7rem;
  color: var(--text-secondary);
  font-weight: 600;
  white-space: nowrap;
}

.disk {
  height: 26px;
  border-radius: 13px;
  position: absolute;
  transition: all 0.5s cubic-bezier(0.4, 0, 0.2, 1);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.8rem;
  font-weight: 800;
  color: white;
  text-shadow: 0 1px 2px rgba(0,0,0,0.5);
  box-shadow: 0 4px 12px rgba(0,0,0,0.5);
  left: 50%;
  transform: translateX(-50%);
  z-index: 10;
  border: 1px solid rgba(255,255,255,0.2);
}

@media (max-width: 600px) {
  .top-nav {
    padding: 0 1rem;
  }
  .nav-brand {
    font-size: 1rem;
  }
  .viz-header {
    flex-direction: column;
    gap: 0.5rem;
    text-align: center;
  }
  .viz-header h1 {
    font-size: 1.5rem;
  }
  .viz-legend {
    margin-left: 0;
    justify-content: center;
    flex-wrap: wrap;
    gap: 0.5rem;
  }
  .rods-container {
    gap: 0.5rem;
  }
  .rod {
    width: 80px;
  }
  .rod-base {
    width: 80px;
  }
  .rod-stem {
    height: 140px;
  }
  .rod-label {
    bottom: -20px;
    font-size: 0.6rem;
  }
  .hanoi-workspace {
    padding-bottom: 25px;
  }
}

@media (max-width: 380px) {
  .rods-container {
    gap: 0.25rem;
  }
  .rod {
    width: 70px;
  }
  .rod-base {
    width: 70px;
  }
}

/* Tree Panel */
.tree-panel { 
    flex: 2;
    background: var(--bg-secondary); 
    border-radius: 12px; 
    border: 1px solid var(--border-color); 
    display: flex; 
    flex-direction: column; 
    padding: 1rem; 
    min-height: 0; /* Important for flex-shrink */
}
.panel-header {
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--text-secondary);
  text-transform: uppercase;
  margin-bottom: 1rem;
}
.tree-viz {
  flex: 1;
  overflow: auto;
  display: flex;
  justify-content: center;
  align-items: flex-start;
}

/* Recursion Tree Nodes */
.tree-node {
  padding: 0.4rem 0.8rem;
  background: #0f172a;
  border: 1px solid var(--border-color);
  border-radius: 4px;
  font-size: 0.7rem;
  white-space: nowrap;
  margin: 0 0.5rem;
  position: relative;
  transition: all 0.3s;
}
.tree-node.active {
  border-color: var(--accent-primary);
  background: rgba(99, 102, 241, 0.1);
  color: var(--accent-primary);
}
.tree-node.completed {
  opacity: 0.6;
}

/* Explanation Side */
.explanation-side {
  background: var(--bg-secondary);
  border-left: 1px solid var(--border-color);
  padding: 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}
.code-block {
  background: #0f172a;
  padding: 1rem;
  border-radius: 8px;
  font-family: "JetBrains Mono", monospace;
  font-size: 0.8rem;
  border: 1px solid var(--border-color);
}
.log-content {
  flex: 1;
  overflow-y: auto;
  background: rgba(0, 0, 0, 0.2);
  border-radius: 8px;
  padding: 0.75rem;
}
.log-entry {
  padding: 0.4rem;
  border-bottom: 1px solid var(--border-color);
  font-size: 0.8rem;
  color: var(--text-secondary);
  animation: fadeIn 0.3s;
}
.log-entry.active {
  color: var(--accent-primary);
  font-weight: 600;
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(5px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}
input[type="range"] {
  width: 100%;
  accent-color: var(--accent-primary);
}
.lang-select {
  background: #0f172a;
  color: white;
  border: 1px solid var(--border-color);
  font-size: 0.75rem;
}