/* ========== Global Reset & Variables ========== */
:root {
  --bg-primary: #ffffff;
  --bg-secondary: #f8f9fa;
  --bg-tertiary: #f1f3f5;
  --text-primary: #1a1a2e;
  --text-secondary: #6c757d;
  --text-tertiary: #adb5bd;
  --border-color: #e0e0e0;
  --accent: #534AB7;
  --accent-light: #EEEDFE;
  --accent-hover: #3C3489;
  --coral: #D85A30;
  --coral-light: #FAECE7;
  --teal: #0F6E56;
  --teal-light: #E1F5EE;
  --amber: #BA7517;
  --amber-light: #FAEEDA;
  --success: #1D9E75;
  --danger: #E24B4A;
  --radius: 10px;
  --radius-sm: 6px;
  --sidebar-width: 280px;
  --shadow: 0 2px 8px rgba(0,0,0,0.08);
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
  --font-mono: "JetBrains Mono", "Cascadia Code", "Fira Code", Consolas, monospace;
}

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

html, body {
  height: 100%;
  font-family: var(--font-sans);
  font-size: 15px;
  color: var(--text-primary);
  background: var(--bg-tertiary);
  overflow: hidden;
}

#app {
  display: flex;
  height: 100%;
}

/* ========== Content Area ========== */
#content {
  flex: 1;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  background: var(--bg-primary);
}

#content-header {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 24px;
  border-bottom: 1px solid var(--border-color);
  background: var(--bg-primary);
  flex-shrink: 0;
}

#sidebar-toggle {
  display: none;
  background: none;
  border: none;
  font-size: 20px;
  cursor: pointer;
  color: var(--text-secondary);
  padding: 4px 8px;
}

#breadcrumb {
  font-size: 14px;
  color: var(--text-secondary);
}

#breadcrumb .crumb-current {
  color: var(--text-primary);
  font-weight: 500;
}

#lesson-container {
  flex: 1;
  overflow-y: auto;
  padding: 32px 48px;
}

/* ========== Lesson Page Layout ========== */
.lesson-section {
  margin-bottom: 40px;
}

.lesson-section h2 {
  font-size: 22px;
  font-weight: 600;
  margin-bottom: 16px;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 8px;
}

.lesson-section h2 .section-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border-radius: 50%;
  background: var(--accent);
  color: white;
  font-size: 14px;
  font-weight: 500;
  flex-shrink: 0;
}

.lesson-section h3 {
  font-size: 17px;
  font-weight: 600;
  margin: 20px 0 10px;
  color: var(--text-primary);
}

.lesson-section p {
  line-height: 1.8;
  margin-bottom: 12px;
  color: var(--text-primary);
}

.lesson-section .formula-block {
  background: var(--bg-secondary);
  border-left: 3px solid var(--accent);
  padding: 16px 20px;
  margin: 16px 0;
  border-radius: 0 var(--radius) var(--radius) 0;
  overflow-x: auto;
}

.lesson-section .note-block {
  background: var(--amber-light);
  border-left: 3px solid var(--amber);
  padding: 12px 16px;
  margin: 16px 0;
  border-radius: 0 var(--radius) var(--radius) 0;
  font-size: 14px;
  color: #633806;
}

/* ========== Interactive Panel ========== */
.interactive-panel {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius);
  padding: 20px;
  margin: 20px 0;
}

.interactive-panel .panel-title {
  font-size: 14px;
  font-weight: 600;
  color: var(--accent);
  margin-bottom: 16px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.canvas-wrapper {
  display: flex;
  justify-content: center;
  align-items: center;
  background: white;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  margin-bottom: 16px;
  overflow: hidden;
  touch-action: none;
}

.canvas-wrapper canvas {
  max-width: 100%;
  height: auto;
}

.demo-hint {
  font-size: 13px;
  color: var(--text-secondary);
  margin-bottom: 12px;
  padding: 8px 14px;
  background: var(--accent-light);
  border-radius: var(--radius-sm);
  line-height: 1.5;
}

.demo-hint kbd {
  display: inline-block;
  padding: 1px 6px;
  font-family: var(--font-mono);
  font-size: 12px;
  background: white;
  border: 1px solid var(--border-color);
  border-radius: 4px;
  box-shadow: 0 1px 0 var(--border-color);
}

canvas {
  display: block;
  cursor: crosshair;
}

/* ========== Controls ========== */
.controls-row {
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  align-items: center;
  margin-bottom: 12px;
}

.control-group {
  display: flex;
  flex-direction: column;
  gap: 6px;
  min-width: 200px;
  flex: 1;
}

.control-group label {
  font-size: 13px;
  color: var(--text-secondary);
  font-weight: 500;
}

.control-group .value-display {
  font-family: var(--font-mono);
  font-size: 14px;
  color: var(--accent);
  font-weight: 600;
}

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

input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: var(--accent);
  cursor: pointer;
  border: 2px solid white;
  box-shadow: 0 1px 4px rgba(0,0,0,0.2);
}

input[type="range"]::-moz-range-thumb {
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: var(--accent);
  cursor: pointer;
  border: 2px solid white;
  box-shadow: 0 1px 4px rgba(0,0,0,0.2);
}

.btn-group {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.btn {
  padding: 8px 16px;
  border: 1px solid var(--border-color);
  background: white;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 13px;
  font-family: var(--font-sans);
  color: var(--text-secondary);
  transition: all 0.2s;
}

.btn:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.btn.active {
  background: var(--accent);
  color: white;
  border-color: var(--accent);
}

/* ========== Data Display ========== */
.data-display {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
  gap: 12px;
  margin-top: 12px;
}

.data-card {
  background: white;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 12px 16px;
  text-align: center;
}

.data-card .label {
  font-size: 12px;
  color: var(--text-tertiary);
  margin-bottom: 4px;
}

.data-card .value {
  font-family: var(--font-mono);
  font-size: 18px;
  font-weight: 600;
  color: var(--accent);
}

/* ========== Code Block ========== */
.code-collapsible {
  margin: 16px 0;
  border: 1px solid var(--border-color);
  border-radius: var(--radius);
  overflow: hidden;
  background: var(--bg-secondary);
}

.code-collapsible > summary {
  list-style: none;
  cursor: pointer;
  padding: 12px 16px;
  font-size: 14px;
  font-weight: 600;
  color: var(--text-secondary);
  user-select: none;
  display: flex;
  align-items: center;
  gap: 8px;
  transition: background 0.15s, color 0.15s;
}

.code-collapsible > summary::-webkit-details-marker {
  display: none;
}

.code-collapsible > summary::before {
  content: '▶';
  font-size: 10px;
  color: var(--accent);
  transition: transform 0.2s ease;
  flex-shrink: 0;
}

.code-collapsible[open] > summary::before {
  transform: rotate(90deg);
}

.code-collapsible > summary:hover {
  background: var(--bg-tertiary, rgba(0, 0, 0, 0.03));
  color: var(--text-primary);
}

.code-collapsible[open] > summary {
  border-bottom: 1px solid var(--border-color);
}

.code-collapsible .code-block {
  margin: 0;
  border-radius: 0;
}

.code-block {
  background: #1e1e2e;
  border-radius: var(--radius);
  padding: 16px 20px;
  margin: 16px 0;
  overflow-x: auto;
}

.code-block pre {
  font-family: var(--font-mono);
  font-size: 13px;
  line-height: 1.7;
  color: #cdd6f4;
}

.code-block .keyword { color: #cba6f7; }
.code-block .string { color: #a6e3a1; }
.code-block .comment { color: #6c7086; font-style: italic; }
.code-block .number { color: #fab387; }
.code-block .func { color: #89b4fa; }

/* ========== Exercise Block ========== */
.exercise-block {
  background: var(--teal-light);
  border-left: 3px solid var(--teal);
  padding: 16px 20px;
  margin: 20px 0;
  border-radius: 0 var(--radius) var(--radius) 0;
}

.exercise-block h4 {
  font-size: 15px;
  font-weight: 600;
  color: var(--teal);
  margin-bottom: 8px;
}

.exercise-block p {
  font-size: 14px;
  color: #085041;
  margin-bottom: 6px;
}

/* ========== Navigation Footer ========== */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 48px;
  padding-top: 24px;
  border-top: 1px solid var(--border-color);
}

.lesson-nav button {
  padding: 10px 20px;
  border: 1px solid var(--border-color);
  background: white;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 14px;
  font-family: var(--font-sans);
  color: var(--text-primary);
  transition: all 0.2s;
}

.lesson-nav button:hover:not(:disabled) {
  background: var(--accent);
  color: white;
  border-color: var(--accent);
}

.lesson-nav button:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

/* ========== Sidebar Backdrop (mobile) ========== */
#sidebar-backdrop {
  display: none;
  position: fixed;
  inset: 0;
  z-index: 99;
  background: rgba(0, 0, 0, 0.3);
  transition: opacity 0.3s;
}

@media (max-width: 768px) {
  #sidebar-backdrop {
    display: block;
    opacity: 0;
    pointer-events: none;
  }
  #sidebar-backdrop.visible {
    opacity: 1;
    pointer-events: auto;
  }
  #sidebar {
    position: fixed;
    left: 0;
    top: 0;
    z-index: 100;
    transform: translateX(-100%);
    transition: transform 0.3s;
  }
  #sidebar.open {
    transform: translateX(0);
  }
  #sidebar-toggle {
    display: block;
  }
  #lesson-container {
    padding: 16px;
  }
  .controls-row {
    flex-direction: column;
    align-items: stretch;
  }
  .control-group {
    min-width: unset;
  }
  .data-display {
    grid-template-columns: repeat(2, 1fr);
  }
  .btn-group .btn {
    flex: 1;
    text-align: center;
  }
}