/* ========================================
   CSS Custom Properties (Variables)
   ======================================== */
:root {
  /* Colors */
  --bg-primary: #2d3748;
  --bg-secondary: #374151;
  --bg-dark: #1a202c;
  --bg-darker: #2b2b2b;
  --bg-modal-overlay: rgba(0, 0, 0, 0.7);
  
  --border-color: #4a5568;
  --border-color-dark: #3d3d3d;
  
  --text-primary: #e2e8f0;
  --text-secondary: #a0aec0;
  --text-muted: #cccccc;
  
  --accent-blue: #63b3ed;
  --accent-blue-light: #90cdf4;
  --accent-blue-dark: #4299e1;
  --accent-blue-godot: #57b3ff;
  --accent-blue-hover: rgba(99, 179, 237, 0.1);
  --accent-blue-focus: rgba(99, 179, 237, 0.2);
  --accent-blue-drop: #2b6cb0;
  
  --accent-mint: #42ffc2;
  --accent-yellow: #ffd942;
  --accent-pink: #ff7085;
  --accent-orange: #ff8142;
  
  /* Error colors */
  --error-red: #e53e3e;
  --error-red-hover: #c53030;
  --error-red-border: #dc2626;
  --error-bg: #2d1b1b;
  --error-bg-dark: #1f1414;
  --error-bg-darker: #1a1414;
  --error-bg-darkest: #0f0a0a;
  --error-text: #fecaca;
  --error-text-light: #fca5a5;
  --error-border-dark: #4c1d1d;
  
  /* Success colors */
  --success-green: #28a745;
  --success-green-hover: #218838;
  --success-green-dark: #1e7e34;
  
  /* Warning colors */
  --warning-orange: #f59e0b;
  --warning-yellow: #fbbf24;
  --warning-bg: #1a1414;
  --warning-bg-light: #2d1b0f;
  --warning-border: #4c2d0f;
  
  /* Neutral colors */
  --disabled-gray: #6c757d;
  --comment-gray: #676767;
  
  /* Spacing */
  --spacing-xxs: 2px;
  --spacing-xs: 0.25rem;  /* 4px */
  --spacing-sm: 0.5rem;   /* 8px */
  --spacing-md: 0.75rem;  /* 12px */
  --spacing-lg: 1rem;     /* 16px */
  --spacing-xl: 1.5rem;   /* 24px */
  --spacing-2xl: 2rem;    /* 32px */
  
  /* Fonts */
  --font-mono: 'Fira Code', 'Cascadia Code', 'JetBrains Mono', 'SF Mono', Consolas, 'Liberation Mono', monospace;
  --font-sans: sans-serif;
  
  /* Transitions */
  --transition-fast: 0.2s ease;
  --transition-normal: 0.25s ease;
  
  /* Shadows */
  --shadow-modal: 0 10px 25px rgba(0, 0, 0, 0.3);
  --shadow-popup: 0 4px 20px rgba(0, 0, 0, 0.5);
  --shadow-focus: 0 0 0 2px var(--accent-blue-focus);
  
  /* Border radius */
  --radius-sm: 3px;
  --radius-md: 4px;
  --radius-lg: 6px;
  --radius-xl: 8px;
  --radius-2xl: 12px;
}

/* ========================================
   Base Styles
   ======================================== */
body {
  font-family: sans-serif;
  margin: 0 auto;
  padding: var(--spacing-lg);
  max-width: 800px;
  background-color: var(--bg-primary);
  color: var(--text-primary);
}

h1, h2 {
  margin-bottom: var(--spacing-sm);
  color: var(--accent-blue);
}

/* ========================================
   Buttons
   ======================================== */
button {
  display: block;
  width: 100%;
  padding: 0.3rem;
  margin: 0.01rem 0;
  font-size: 1rem;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-xl);
  background-color: var(--bg-secondary);
  color: var(--text-primary);
  cursor: pointer;
  transition: background-color var(--transition-fast), border-color var(--transition-fast);
}

button:hover {
  background-color: var(--border-color);
}

button:focus-visible {
  outline: 2px solid var(--accent-blue);
  outline-offset: 2px;
}

/* Button Variants */
.schedule-action-btn,
.new-lesson-btn {
  width: 110px;
  min-width: 110px;
  max-width: 110px;
  box-sizing: border-box;
}

.insert-day-btn {
  font-size: 0.9em;
  width: auto !important;
  min-width: auto !important;
  max-width: none !important;
  white-space: nowrap;
  padding: var(--spacing-xxs) var(--spacing-sm) !important;
}

.delete-btn {
  background-color: var(--error-red);
  color: white;
  border: 1px solid var(--error-red);
  padding: var(--spacing-sm) var(--spacing-lg);
  border-radius: var(--radius-md);
  cursor: pointer;
  font-size: 14px;
}

.delete-btn:hover {
  background-color: var(--error-red-hover);
  border-color: var(--error-red-hover);
}

.delete-btn:disabled {
  background-color: var(--disabled-gray);
  border-color: var(--disabled-gray);
  cursor: not-allowed;
  opacity: 0.6;
}

.lesson-cluster-bottom .delete-btn {
  width: auto !important;
  min-width: auto !important;
  max-width: none !important;
  padding: 2px 6px !important;
  font-size: 11px !important;
  height: auto !important;
  min-height: auto !important;
  line-height: 1.2 !important;
}

.delete-day-btn {
  width: auto !important;
  min-width: auto !important;
  max-width: none !important;
  padding: var(--spacing-sm) var(--spacing-md) !important;
  font-size: 14px !important;
  height: 100% !important;
  min-height: 60px !important;
  display: flex !important;
  align-items: center !important;
  justify-content: center !important;
  background-color: var(--error-red);
  color: white;
  border: 1px solid var(--error-red);
  border-radius: var(--radius-md);
  cursor: pointer;
}

.delete-day-btn:hover {
  background-color: var(--error-red-hover);
  border-color: var(--error-red-hover);
}

.go-to-today-btn {
  background-color: var(--success-green) !important;
  border-color: var(--success-green) !important;
  color: white !important;
}

.go-to-today-btn:hover {
  background-color: var(--success-green-hover) !important;
  border-color: var(--success-green-dark) !important;
}

.date-offset-control button {
  width: auto !important;
  min-width: auto !important;
  padding: var(--spacing-xxs) var(--spacing-md) !important;
  margin: 0 !important;
  font-size: 0.9rem !important;
  background-color: var(--border-color);
  color: var(--text-primary);
  border: 1px solid var(--border-color);
}

.date-offset-control button:hover {
  background-color: var(--accent-blue);
  color: var(--bg-dark);
  border-color: var(--accent-blue);
}

.lesson-popup-result-btn {
  text-align: left;
  white-space: nowrap;
  width: 100% !important;
  min-width: 100% !important;
  max-width: 100% !important;
  overflow: hidden;
  text-overflow: ellipsis;
  box-sizing: border-box;
  display: block !important;
  margin: var(--spacing-xxs) 0 !important;
  padding: var(--spacing-sm) var(--spacing-md) !important;
  min-height: 36px;
}

.lesson-main-btn {
  font-weight: bold;
  min-width: 200px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

/* ========================================
   Links
   ======================================== */
a.schedule-action-btn {
  display: block;
  text-decoration: none;
  color: var(--text-primary);
  padding: 0.3rem;
  margin: 0.01rem 0;
  font-size: 1rem;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-xl);
  background-color: var(--bg-secondary);
  cursor: pointer;
  transition: background-color var(--transition-fast);
  text-align: center;
}

a.schedule-action-btn:focus-visible {
  outline: 2px solid var(--accent-blue);
  outline-offset: 2px;
}

a.schedule-action-btn:hover {
  background-color: var(--border-color);
}

.class-link {
  display: block;
  text-decoration: none;
  color: var(--accent-blue);
  padding: var(--spacing-sm) 0;
  margin: var(--spacing-xs) 0;
  font-size: 1.1rem;
  border-bottom: 1px solid var(--border-color);
  transition: color var(--transition-fast);
}

.class-link:hover {
  color: var(--accent-blue-light);
  text-decoration: underline;
}

.class-link-inactive {
  display: block;
  color: var(--text-secondary);
  padding: var(--spacing-sm) 0;
  margin: var(--spacing-xs) 0;
  font-size: 1.1rem;
  border-bottom: 1px solid var(--border-color);
  font-style: italic;
}

/* Navigation links between pages (teacher.html and editor.html) */
a:not(.class-link):not(.schedule-action-btn) {
  color: var(--accent-blue);
  text-decoration: none;
  padding: 0.3rem 0;
  border-bottom: 1px solid var(--border-color);
  transition: color var(--transition-fast);
  display: inline-block;
}

a:not(.class-link):not(.schedule-action-btn):hover {
  color: var(--accent-blue-light);
  text-decoration: underline;
}

/* Lesson link styles */
.lesson-link {
  color: var(--accent-blue);
  text-decoration: none;
  border-bottom: 1px dotted var(--accent-blue);
  transition: all var(--transition-fast);
}

.lesson-link:hover {
  color: var(--accent-blue-light);
  border-bottom: 1px solid var(--accent-blue-light);
}

.lesson-link:active {
  color: var(--accent-blue-dark);
  border-bottom-color: var(--accent-blue-dark);
}

/* ========================================
   Forms
   ======================================== */
textarea {
  background-color: var(--bg-secondary);
  color: var(--text-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-xl);
  padding: var(--spacing-md);
  font-family: var(--font-mono);
  font-size: 14px;
  resize: vertical;
  transition: border-color var(--transition-fast);
  white-space: pre;
  tab-size: 4;
}

textarea:focus-visible {
  outline: 2px solid var(--accent-blue);
  outline-offset: 2px;
}

#dslInput {
  font-family: var(--font-mono);
  font-variant-ligatures: none;
  letter-spacing: 0.3px;
  line-height: 1.5;
}

#dslInput:focus,
textarea:focus {
  outline: none;
  border-color: var(--accent-blue);
}

#dslInput:focus-visible,
textarea:focus-visible {
  outline: 2px solid var(--accent-blue);
  outline-offset: 2px;
}

#dslInput:focus {
  background-color: var(--bg-secondary);
}

select,
#aiClassSelect,
#learningObjectives {
  width: 100%;
  padding: var(--spacing-md);
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  color: var(--text-primary);
  font-size: 1rem;
  cursor: pointer;
  transition: border-color var(--transition-fast), background-color var(--transition-fast);
}

select:focus,
select:hover,
#aiClassSelect:focus,
#learningObjectives:focus {
  outline: none;
  border-color: var(--accent-blue);
}

select:focus-visible,
#aiClassSelect:focus-visible,
#learningObjectives:focus-visible {
  outline: 2px solid var(--accent-blue);
  outline-offset: 2px;
}

select:focus,
#aiClassSelect:focus,
#learningObjectives:focus {
  background-color: var(--bg-primary);
  box-shadow: var(--shadow-focus);
}

#learningObjectives {
  resize: vertical;
  min-height: 100px;
  font-family: inherit;
}

.radio-group {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
}

.radio-label {
  display: flex;
  align-items: flex-start;
  gap: var(--spacing-sm);
  cursor: pointer;
  padding: var(--spacing-md);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  transition: all var(--transition-fast);
}

.radio-label:hover {
  border-color: var(--accent-blue);
  background-color: var(--accent-blue-hover);
}

.radio-label input[type="radio"] {
  margin: 0;
  accent-color: var(--accent-blue);
}

.radio-label span {
  font-weight: 600;
  color: var(--accent-blue);
}

.date-offset-control {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.95rem;
}

.date-offset-control label {
  font-weight: 500;
  color: var(--text-primary);
}

.current-offset-display {
  font-weight: bold;
  color: var(--text-primary);
  background-color: var(--bg-secondary);
  padding: var(--spacing-xxs) var(--spacing-sm);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  font-size: 0.9rem;
  white-space: nowrap;
}

.date-offset-control input[type="number"] {
  padding: var(--spacing-xxs) var(--spacing-sm);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  font-size: 0.9rem;
  background-color: var(--bg-dark);
  color: var(--text-primary);
}

.date-offset-control input[type="number"]:focus {
  outline: none;
  border-color: var(--accent-blue);
  background-color: var(--bg-primary);
}

.date-offset-control input[type="number"]:focus-visible {
  outline: 2px solid var(--accent-blue);
  outline-offset: 2px;
}

/* ========================================
   Modals and Popups
   ======================================== */
.modal {
  position: fixed !important;
  inset: 0 !important;
  width: 100vw !important;
  height: 100vh !important;
  margin: 0 !important;
  max-width: none !important;
  max-height: none !important;
  z-index: 1000;
  background-color: var(--bg-modal-overlay);
  backdrop-filter: blur(4px);
  display: flex;
  align-items: center;
  justify-content: center;
}

.modal-content {
  background-color: var(--bg-primary);
  padding: var(--spacing-2xl) var(--spacing-xl);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-2xl);
  max-width: 400px;
  width: auto;
  box-sizing: border-box;
  max-height: 85vh;
  overflow-y: auto;
  box-shadow: var(--shadow-modal);
  display: flex;
  flex-direction: column;
  align-items: stretch;
  margin: 0 !important;
}

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

.modal-body {
  padding: var(--spacing-xl);
}

.lesson-popup {
  position: fixed;
  inset: 0;
  background: var(--bg-modal-overlay);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 1000;
}

.lesson-popup-box {
  background: var(--bg-primary);
  color: var(--text-primary);
  border: 1px solid var(--border-color);
  padding: var(--spacing-xl);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-popup);
  min-width: 320px;
  max-width: 90vw;
  max-height: 80vh;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  gap: var(--spacing-sm);
}

.lesson-popup-close,
.popup-close-btn {
  align-self: flex-end;
}

.lesson-popup-search {
  margin-bottom: var(--spacing-sm);
  padding: var(--spacing-xxs);
  font-size: 1em;
  background-color: var(--bg-secondary);
  color: var(--text-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
}

.lesson-popup-results {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-xxs);
  max-height: 50vh;
  overflow-y: auto;
}

/* ========================================
   Layout Components
   ======================================== */
#class-list {
  display: flex;
  flex-direction: column;
  gap: 0;
}

#content {
  padding: var(--spacing-lg);
}

#schedulePane {
  width: 100%;
  max-width: 1600px;
  margin: 0 auto;
  transition: width var(--transition-fast);
  background-color: var(--bg-dark);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-xl);
}

#scheduleTable {
  width: 100%;
  min-width: 600px;
  background-color: var(--bg-dark);
  color: var(--text-primary);
}

td {
  position: relative;
  border-bottom: 1px solid var(--border-color);
  padding: var(--spacing-sm);
}

td > * {
  pointer-events: auto;
}

/* Flex utilities */
.flex-row {
  display: flex;
  flex-wrap: nowrap;
  align-items: center;
  gap: 4px;
}

.flex-column {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.flex-row-buttons {
  display: flex;
  gap: 4px;
}

.lessons-cell {
  display: flex;
  flex-wrap: nowrap;
  align-items: center;
  gap: 4px;
  min-height: 48px;
  flex: 1 1 auto;
  position: relative;
}

.lessons-end-buttons {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-xxs);
  align-items: stretch;
  flex-shrink: 0;
}

.insert-day-cell {
  text-align: center;
  padding: var(--spacing-xxs);
}

.schedule-list-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

/* Lesson cluster styles */
.lesson-cluster {
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  border: 2px solid var(--border-color);
  border-radius: var(--radius-xl);
  padding: var(--spacing-xxs) var(--radius-lg);
  margin-right: var(--radius-lg);
  background: var(--bg-secondary);
  color: var(--text-primary);
  box-shadow: 1px 1px 3px var(--bg-dark);
  cursor: grab;
  min-width: 140px;
  font-weight: normal;
}

.lesson-cluster * {
  font-weight: normal;
}

.lesson-cluster-top {
  display: flex;
  justify-content: center;
}

.lesson-cluster-bottom {
  display: flex;
  justify-content: center;
  gap: var(--spacing-xxs);
  margin-top: var(--spacing-xxs);
}

.td-drop-hover {
  background: var(--accent-blue-drop) !important;
}

.today-row {
  background-color: var(--bg-primary) !important;
  border: 2px solid var(--accent-blue) !important;
}

/* ========================================
   Lists
   ======================================== */
ul {
  list-style: none;
  padding-left: 0;
}

li button {
  margin-left: var(--spacing-sm);
}

/* ========================================
   Code and Pre
   ======================================== */
code:not(.lesson-content code) {
  background-color: var(--bg-secondary);
  color: var(--accent-blue-light);
  padding: var(--spacing-xxs) var(--spacing-md);
  border-radius: var(--radius-md);
  font-family: var(--font-mono);
  font-size: 0.9em;
  border: 1px solid var(--border-color);
}

pre:not(.lesson-code) {
  background-color: var(--bg-darker);
  color: var(--text-muted);
  padding: var(--spacing-md);
  border-radius: var(--radius-lg);
}

.lesson-code {
  background-color: var(--bg-darker) !important;
  color: var(--text-muted) !important;
  padding: var(--spacing-md);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-color-dark) !important;
  overflow-x: auto;
  white-space: pre;
  font-family: var(--font-mono);
  font-size: 14px;
  tab-size: 4;
  line-height: 1.4;
  margin-bottom: var(--spacing-md);
  position: relative;
  box-shadow: none !important;
}

/* Prism.js syntax highlighting overrides */
.lesson-code code[class*="language-"] {
  background: transparent !important;
  color: inherit;
  font-family: inherit;
  font-size: inherit;
  line-height: inherit;
  padding: 0 !important;
  border: none !important;
  border-radius: 0 !important;
}

.lesson-code pre[class*="language-"] {
  background: transparent !important;
  padding: 0 !important;
  margin: 0 !important;
  border-radius: 0 !important;
  border: none !important;
  overflow: visible !important;
}

.lesson-content .lesson-code,
.lesson-preview .lesson-code,
pre.lesson-code,
pre[class*="language-"].lesson-code,
.lesson-code pre[class*="language-"],
code[class*="language-"],
pre[class*="language-"],
.lesson-content pre.lesson-code,
.lesson-preview pre.lesson-code {
  background-color: var(--bg-darker) !important;
  border-color: var(--border-color-dark) !important;
  box-shadow: none !important;
  text-shadow: none !important;
}

.lesson-code[data-language]::before {
  content: attr(data-language);
  position: absolute;
  top: var(--spacing-xxs);
  right: var(--spacing-sm);
  background-color: var(--border-color-dark);
  color: var(--text-muted);
  padding: var(--spacing-xxs) var(--spacing-md);
  border-radius: var(--radius-sm);
  font-size: 11px;
  font-family: var(--font-sans);
  text-transform: uppercase;
  font-weight: 500;
  letter-spacing: 0.5px;
  opacity: 0.9;
  z-index: 1;
}

/* Prism.js token colors for Godot dark theme */
.lesson-code .token.comment,
.lesson-code .token.prolog,
.lesson-code .token.doctype,
.lesson-code .token.cdata {
  color: var(--comment-gray);
  font-style: italic;
}

.lesson-code .token.punctuation {
  color: var(--text-muted);
}

.lesson-code .token.property,
.lesson-code .token.tag,
.lesson-code .token.boolean,
.lesson-code .token.number,
.lesson-code .token.constant,
.lesson-code .token.symbol,
.lesson-code .token.deleted,
.lesson-code .token.type-hint,
.lesson-code .token.builtin-type {
  color: var(--accent-mint);
}

.lesson-code .token.selector,
.lesson-code .token.attr-name,
.lesson-code .token.string,
.lesson-code .token.char,
.lesson-code .token.builtin,
.lesson-code .token.inserted {
  color: var(--accent-yellow);
}

.lesson-code .token.operator,
.lesson-code .token.entity,
.lesson-code .token.url,
.lesson-code .language-css .token.string,
.lesson-code .style .token.string {
  color: var(--text-muted);
}

.lesson-code .token.atrule,
.lesson-code .token.attr-value,
.lesson-code .token.keyword,
.lesson-code .token.annotation,
.lesson-code .token.decorator {
  color: var(--accent-pink);
}

.lesson-code .token.function,
.lesson-code .token.class-name,
.lesson-code .token.namespace {
  color: var(--accent-blue-godot);
}

.lesson-code .token.regex,
.lesson-code .token.important,
.lesson-code .token.variable {
  color: var(--accent-orange);
}

/* Inline code styling (applies to code tags within lesson-content) */
.lesson-content code {
  background-color: var(--bg-secondary);
  color: var(--accent-blue-light);
  padding: var(--spacing-xxs) var(--spacing-xs);
  border-radius: var(--radius-md);
  font-family: var(--font-mono);
  font-size: 0.9em;
  border: 1px solid var(--border-color);
}

/* ========================================
   Lesson Content Styling
   ======================================== */
.lesson-content {
  color: var(--text-primary);
  line-height: 1.6;
}

.lesson-preview {
  border: 1px solid var(--border-color);
  border-radius: var(--radius-xl);
  padding: var(--spacing-xl);
  margin-top: var(--spacing-sm);
  background-color: var(--bg-primary);
  min-height: 300px;
  max-height: 500px;
  overflow-y: auto;
}

.lesson-title {
  color: var(--accent-blue);
  margin-top: 0;
  margin-bottom: var(--spacing-lg);
  font-size: 2em;
  font-weight: bold;
  border-bottom: 2px solid var(--border-color);
  padding-bottom: var(--spacing-sm);
}

.lesson-heading {
  margin: 1.5em 0 0.75em;
  line-height: 1.2;
  font-weight: 600;
}

.lesson-h1 {
  font-size: 1.8em;
  color: var(--accent-blue-godot);
  border-bottom: 2px solid var(--border-color);
  padding-bottom: 0.3em;
}

.lesson-h2 {
  font-size: 1.5em;
  color: var(--accent-mint);
}

.lesson-h3 {
  font-size: 1.3em;
  color: var(--accent-yellow);
}

.lesson-h4 {
  font-size: 1.1em;
  color: var(--accent-pink);
}

.lesson-h5 {
  font-size: 1em;
  color: var(--accent-orange);
}

.lesson-h6 {
  font-size: 0.9em;
  color: var(--text-muted);
  font-style: italic;
}

.lesson-text {
  color: var(--text-primary);
  line-height: 1.6;
  margin-bottom: var(--spacing-md);
}

.lesson-list {
  color: var(--text-primary);
  line-height: 1.2;
  margin: var(--spacing-sm) 0;
  padding-left: 2em;
}

.lesson-list-item {
  margin-bottom: var(--radius-lg);
}

ul.lesson-list {
  list-style-type: disc;
}

ul.lesson-list .lesson-list-item::marker,
ol.lesson-list .lesson-list-item::marker {
  color: var(--accent-blue);
}

ol.lesson-list {
  list-style-type: decimal;
}

.lesson-separator {
  border: none;
  border-top: 2px solid var(--border-color);
  margin: var(--spacing-xl) 0;
}

/* Collapsible Sections */
.lesson-collapsible {
  margin: var(--spacing-md) 0;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  background-color: transparent;
}

.lesson-collapsible-summary {
  cursor: pointer;
  padding: var(--spacing-sm) var(--spacing-md);
  list-style: none;
  display: flex;
  align-items: center;
  color: var(--accent-blue);
  transition: background-color var(--transition-fast), color var(--transition-fast);
  border-radius: var(--radius-md);
}

.lesson-collapsible-summary::before {
  content: "";
  margin-right: var(--spacing-sm);
  transition: transform var(--transition-fast);
  display: inline-block;
  width: 0;
  height: 0;
  border-style: solid;
  border-width: 4px 0 4px 6px;
  border-color: transparent transparent transparent currentColor;
  vertical-align: middle;
}

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

.lesson-collapsible-summary:hover {
  background-color: var(--accent-blue-hover);
}

.lesson-collapsible-summary-empty {
  min-height: 1.5em;
  min-width: 2em;
}

.collapsible-content {
  padding: var(--spacing-md) var(--spacing-lg);
  padding-top: 0px;
  padding-left: calc(var(--spacing-lg) + 1.5em);
}

/* Nested collapsibles */
.lesson-collapsible .lesson-collapsible {
  margin-left: var(--spacing-lg);
  border-left: 2px solid var(--border-color);
  padding-left: var(--spacing-md);
}

/* ========================================
   Utility Components
   ======================================== */
#contentId {
  font-family: var(--font-mono) !important;
  background-color: var(--bg-secondary) !important;
  color: var(--text-primary) !important;
  padding: var(--spacing-sm) var(--spacing-md) !important;
  border: 1px solid var(--border-color) !important;
  border-radius: var(--radius-xl) !important;
  height: 1.2em !important;
  line-height: 1.2 !important;
  display: inline-flex !important;
  align-items: center !important;
  min-width: 200px !important;
  box-sizing: border-box !important;
}

#loading-state {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--spacing-lg);
  padding: var(--spacing-2xl) 0;
}

.loading-spinner {
  width: 40px;
  height: 40px;
  border: 3px solid var(--border-color);
  border-top: 3px solid var(--accent-blue);
  border-radius: 50%;
  animation: spin 1s linear infinite;
}

@keyframes spin {
  0% { transform: rotate(0deg); }
  100% { transform: rotate(360deg); }
}

.loading-text {
  color: var(--text-secondary);
  font-size: 1.1rem;
  margin: 0;
}

.skeleton-items {
  width: 100%;
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
}

.skeleton-item {
  height: 2.5rem;
  background: linear-gradient(90deg, var(--bg-secondary) 25%, var(--border-color) 50%, var(--bg-secondary) 75%);
  background-size: 200% 100%;
  animation: skeleton-loading 1.5s infinite;
  border-radius: 8px;
  border-bottom: 1px solid var(--border-color);
}

@keyframes skeleton-loading {
  0% { background-position: 200% 0; }
  100% { background-position: -200% 0; }
}

/* ========================================
   Error Display
   ======================================== */
.error-container {
  background-color: var(--error-bg);
  border: 2px solid var(--error-red-border);
  border-radius: var(--radius-xl);
  padding: var(--spacing-xl);
  margin: var(--spacing-sm) 0;
  color: var(--error-text);
}

.error-title {
  color: var(--error-text-light);
  margin-top: 0;
  margin-bottom: var(--spacing-md);
  font-size: 1.2em;
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
}

.error-message {
  background-color: var(--error-bg-dark);
  padding: var(--spacing-sm);
  border-radius: var(--radius-md);
  border-left: 4px solid var(--error-red-border);
  margin-bottom: var(--spacing-lg);
  font-family: var(--font-mono);
}

.error-explanation {
  background-color: var(--error-bg-darker);
  padding: var(--spacing-md);
  border-radius: var(--radius-lg);
  margin-bottom: var(--spacing-lg);
}

.error-explanation p {
  margin-bottom: var(--spacing-sm);
  line-height: 1.5;
}

.error-example {
  margin-top: var(--spacing-md);
}

.error-example pre {
  background-color: var(--error-bg-darkest);
  border: 1px solid var(--error-border-dark);
  border-radius: var(--radius-md);
  padding: var(--spacing-sm);
  margin-top: var(--spacing-sm);
  font-size: 14px;
  overflow-x: auto;
}

.error-example code {
  color: var(--error-text-light);
  background: transparent;
  border: none;
  padding: 0;
}

.error-help {
  background-color: var(--warning-bg);
  padding: var(--spacing-md);
  border-radius: var(--radius-lg);
  border-left: 4px solid var(--warning-orange);
}

.error-help ul {
  margin: var(--spacing-sm) 0 0 20px;
  padding: 0;
}

.error-help li {
  margin-bottom: var(--radius-lg);
  line-height: 1.4;
}

.error-help code {
  background-color: var(--warning-bg-light);
  color: var(--warning-yellow);
  padding: var(--spacing-xxs) var(--spacing-xxs);
  border-radius: var(--radius-sm);
  border: 1px solid var(--warning-border);
}

/* ========================================
   Responsive
   ======================================== */
@media (max-width: 600px) {
  button {
    font-size: 1rem;
    padding: 0.8rem;
  }
}