/* ==========================================================================
   SentenceBuilder - High Contrast, Clean Typography, Zero External Fonts
   System Font Stack: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto
   ========================================================================== */

:root {
  --font-main: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", monospace;

  /* High Contrast Light Palette */
  --bg-app: #f8fafc;
  --bg-surface: #ffffff;
  --bg-surface-alt: #f1f5f9;
  --bg-sidebar: #ffffff;
  --border-color: #cbd5e1;
  --border-focus: #2563eb;
  
  --text-main: #0f172a;
  --text-muted: #475569;
  --text-subtle: #64748b;
  --text-inverse: #ffffff;

  --color-primary: #1d4ed8;
  --color-primary-hover: #1e40af;
  --color-primary-bg: #eff6ff;

  --color-success: #15803d;
  --color-success-bg: #f0fdf4;
  --color-success-border: #86efac;

  --color-warning: #b45309;
  --color-warning-bg: #fffbeb;
  --color-warning-border: #fcd34d;

  --color-danger: #b91c1c;
  --color-danger-bg: #fef2f2;
  --color-danger-border: #fca5a5;

  --color-purple: #6d28d9;
  --color-purple-bg: #f5f3ff;

  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -2px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -4px rgba(0, 0, 0, 0.1);

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;
  --radius-full: 9999px;

  --level-1: #2563eb;
  --level-2: #059669;
  --level-3: #d97706;
  --level-4: #7c3aed;
}

[data-theme="dark"] {
  /* High Contrast Dark Palette */
  --bg-app: #090d16;
  --bg-surface: #111827;
  --bg-surface-alt: #1f2937;
  --bg-sidebar: #0f172a;
  --border-color: #334155;
  --border-focus: #60a5fa;

  --text-main: #f8fafc;
  --text-muted: #cbd5e1;
  --text-subtle: #94a3b8;
  --text-inverse: #090d16;

  --color-primary: #3b82f6;
  --color-primary-hover: #60a5fa;
  --color-primary-bg: #1e293b;

  --color-success: #22c55e;
  --color-success-bg: #064e3b;
  --color-success-border: #059669;

  --color-warning: #f59e0b;
  --color-warning-bg: #78350f;
  --color-warning-border: #d97706;

  --color-danger: #ef4444;
  --color-danger-bg: #7f1d1d;
  --color-danger-border: #dc2626;

  --color-purple: #a855f7;
  --color-purple-bg: #2e1065;

  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.4);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.5);

  --level-1: #60a5fa;
  --level-2: #34d399;
  --level-3: #fbbf24;
  --level-4: #c084fc;
}

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

html, body {
  font-family: var(--font-main);
  background-color: var(--bg-app);
  color: var(--text-main);
  line-height: 1.5;
  font-size: 15px;
  -webkit-font-smoothing: antialiased;
  min-height: 100vh;
}

/* Layout */
.app-container {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

/* Header */
.app-header {
  background: var(--bg-surface);
  border-bottom: 2px solid var(--border-color);
  padding: 0.75rem 1.5rem;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  position: sticky;
  top: 0;
  z-index: 40;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.brand-icon {
  font-size: 1.5rem;
  background: var(--color-primary-bg);
  border: 1px solid var(--border-color);
  width: 40px;
  height: 40px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-md);
}

.brand-title {
  font-size: 1.25rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--text-main);
}

.brand-badge {
  font-size: 0.75rem;
  font-weight: 700;
  background: var(--bg-surface-alt);
  border: 1px solid var(--border-color);
  padding: 2px 8px;
  border-radius: var(--radius-full);
  color: var(--text-muted);
}

.header-center {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.topic-badge-btn {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  background: var(--bg-surface-alt);
  border: 1.5px solid var(--border-color);
  color: var(--text-main);
  padding: 0.45rem 0.9rem;
  border-radius: var(--radius-md);
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.15s ease;
}

.topic-badge-btn:hover {
  border-color: var(--color-primary);
  background: var(--color-primary-bg);
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

/* Main Split View */
.app-main {
  display: grid;
  grid-template-columns: 360px minmax(0, 1fr);
  flex: 1;
  min-height: calc(100vh - 65px);
}

@media (max-width: 1024px) {
  .app-main {
    grid-template-columns: 320px minmax(0, 1fr);
  }
}

@media (max-width: 860px) {
  .app-main {
    grid-template-columns: minmax(0, 1fr);
  }
}

/* Left Sidebar: Vocabulary & Pool */
.sidebar {
  background: var(--bg-sidebar);
  border-right: 2px solid var(--border-color);
  display: flex;
  flex-direction: column;
  height: calc(100vh - 65px);
  position: sticky;
  top: 65px;
  overflow: hidden;
  min-width: 0;
}

.sidebar-header {
  padding: 1rem;
  border-bottom: 1.5px solid var(--border-color);
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  background: var(--bg-surface);
}

.sidebar-title-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.sidebar-title {
  font-size: 1rem;
  font-weight: 700;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.search-input-wrap {
  position: relative;
}

.search-input {
  width: 100%;
  padding: 0.55rem 0.75rem 0.55rem 2rem;
  border: 1.5px solid var(--border-color);
  border-radius: var(--radius-sm);
  background: var(--bg-app);
  color: var(--text-main);
  font-size: 0.88rem;
  outline: none;
  font-family: inherit;
  transition: border-color 0.15s;
}

.search-input:focus {
  border-color: var(--border-focus);
}

.search-icon {
  position: absolute;
  left: 0.65rem;
  top: 50%;
  transform: translateY(-50%);
  color: var(--text-subtle);
  pointer-events: none;
  font-size: 0.85rem;
}

/* Frequency filter pills */
.freq-filter-bar {
  display: flex;
  gap: 0.35rem;
  overflow-x: auto;
  padding-bottom: 2px;
}

.freq-pill {
  padding: 3px 8px;
  font-size: 0.75rem;
  font-weight: 600;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-full);
  background: var(--bg-surface-alt);
  color: var(--text-muted);
  cursor: pointer;
  white-space: nowrap;
  transition: all 0.15s;
}

.freq-pill:hover, .freq-pill.active {
  background: var(--text-main);
  color: var(--text-inverse);
  border-color: var(--text-main);
}

/* Accordion controls row */
.sidebar-tree-controls {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  flex-wrap: wrap;
}

.btn-tree-control {
  padding: 3px 9px;
  font-size: 0.72rem;
  font-weight: 700;
  font-family: inherit;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-full);
  background: var(--bg-surface);
  color: var(--text-muted);
  cursor: pointer;
  transition: all 0.15s ease;
}

.btn-tree-control:hover {
  border-color: var(--text-main);
  color: var(--text-main);
  background: var(--bg-surface-alt);
}

.btn-tree-control:focus-visible {
  outline: 2px solid var(--border-focus);
  outline-offset: 1px;
}

.tree-result-count {
  margin-left: auto;
  font-size: 0.72rem;
  color: var(--text-subtle);
}

/* Empty state inside the vocabulary tree */
.vocab-empty-state {
  padding: 2rem 1rem;
  text-align: center;
  color: var(--text-subtle);
  flex-shrink: 0;
}

.vocab-empty-title {
  font-weight: 700;
  margin-bottom: 0.5rem;
}

.vocab-empty-sub {
  font-size: 0.85rem;
}

/* Vocabulary Tree Container */
.vocab-tree {
  flex: 1;
  overflow-y: auto;
  padding: 0.75rem;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.vocab-block {
  border: 1.5px solid var(--border-color);
  border-radius: var(--radius-md);
  background: var(--bg-surface);
  overflow: hidden;
  /* Flex child inside .vocab-tree: never squash blocks, let the tree scroll */
  flex-shrink: 0;
}

.vocab-block-header {
  width: 100%;
  padding: 0.65rem 0.85rem;
  background: var(--bg-surface-alt);
  border: none;
  border-bottom: 1px solid transparent;
  color: var(--text-main);
  font-family: inherit;
  font-weight: 700;
  font-size: 0.88rem;
  text-align: left;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
  user-select: none;
}

.vocab-block-header:focus-visible {
  outline: 2px solid var(--border-focus);
  outline-offset: -2px;
}

.vocab-block.open .vocab-block-header {
  border-bottom-color: var(--border-color);
}

.vocab-block-title {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.vocab-block-meta {
  display: flex;
  align-items: center;
  gap: 0.45rem;
  flex-shrink: 0;
}

.vocab-block-chevron {
  font-size: 0.72rem;
  line-height: 1;
  color: var(--text-subtle);
  transition: transform 0.15s ease;
}

.vocab-block:not(.open) .vocab-block-chevron {
  transform: rotate(-90deg);
}

/* Collapsible body is driven purely by the .open class (no inline styles) */
.vocab-block .vocab-subblocks-wrap {
  display: none;
}

.vocab-block.open .vocab-subblocks-wrap {
  display: block;
}

.vocab-block-badge {
  font-size: 0.7rem;
  padding: 1px 6px;
  background: var(--border-color);
  border-radius: var(--radius-full);
  color: var(--text-main);
  font-weight: 700;
}

.vocab-subblock {
  padding: 0.5rem 0.75rem;
  border-bottom: 1px dashed var(--border-color);
}

.vocab-subblock:last-child {
  border-bottom: none;
}

.vocab-subblock-title {
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--text-subtle);
  margin-bottom: 0.45rem;
}

.vocab-items-grid {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}

.vocab-card {
  padding: 0.45rem 0.65rem;
  background: var(--bg-app);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
  cursor: pointer;
  transition: all 0.15s ease;
}

.vocab-card:hover {
  border-color: var(--color-primary);
  background: var(--color-primary-bg);
}

.vocab-card:focus-visible {
  outline: 2px solid var(--border-focus);
  outline-offset: 1px;
}

.vocab-card.in-pool {
  border-color: var(--color-success);
  background: var(--color-success-bg);
}

.vocab-card-content {
  flex: 1;
  min-width: 0;
}

.vocab-card-word {
  font-weight: 700;
  font-size: 0.9rem;
  color: var(--text-main);
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.vocab-card-translation {
  font-size: 0.75rem;
  color: var(--text-muted);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.vocab-card-meta {
  font-size: 0.7rem;
  color: var(--text-subtle);
  font-style: italic;
}

.vocab-freq-stars {
  font-size: 0.72rem;
  color: #d97706;
  white-space: nowrap;
}

.btn-add-pool {
  background: var(--bg-surface);
  border: 1.5px solid var(--border-color);
  color: var(--text-main);
  width: 28px;
  height: 28px;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  font-weight: 700;
  font-size: 1rem;
  transition: all 0.15s;
  flex-shrink: 0;
}

.btn-add-pool:hover {
  background: var(--color-primary);
  color: var(--text-inverse);
  border-color: var(--color-primary);
}

.btn-add-pool.in-pool {
  background: var(--color-success);
  color: var(--text-inverse);
  border-color: var(--color-success);
}

/* Sticky Word Pool Box at bottom of sidebar */
.word-pool-drawer {
  background: var(--bg-surface);
  border-top: 2px solid var(--border-color);
  padding: 0.85rem;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
  box-shadow: 0 -4px 10px rgba(0, 0, 0, 0.05);
}

.pool-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.pool-title {
  font-size: 0.88rem;
  font-weight: 800;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.pool-count-badge {
  background: var(--color-primary-bg);
  color: var(--color-primary);
  border: 1px solid var(--color-primary);
  font-size: 0.72rem;
  font-weight: 800;
  padding: 1px 7px;
  border-radius: var(--radius-full);
}

.pool-chips-container {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
  max-height: 105px;
  overflow-y: auto;
  padding: 2px;
}

.pool-chip {
  background: var(--bg-surface-alt);
  border: 1px solid var(--border-color);
  color: var(--text-main);
  padding: 3px 8px;
  border-radius: var(--radius-full);
  font-size: 0.8rem;
  font-weight: 600;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.pool-chip-remove {
  cursor: pointer;
  color: var(--text-subtle);
  font-weight: 700;
  font-size: 0.9rem;
}

.pool-chip-remove:hover {
  color: var(--color-danger);
}

.pool-empty-msg {
  font-size: 0.78rem;
  color: var(--text-subtle);
  text-align: center;
  padding: 0.5rem 0;
  font-style: italic;
}

.pool-actions {
  display: flex;
  gap: 0.4rem;
}

/* Center Content: Workspace & Builder */
.builder-workspace {
  padding: 1.5rem 2rem;
  max-width: 960px;
  margin: 0 auto;
  width: 100%;
  min-width: 0;
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

/* Stepper Progress Bar */
.stepper-nav {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 0.75rem;
}

.step-card {
  background: var(--bg-surface);
  border: 2px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 0.75rem;
  cursor: pointer;
  transition: all 0.15s ease;
  position: relative;
  text-align: left;
}

.step-card.active {
  border-color: var(--color-primary);
  background: var(--color-primary-bg);
  box-shadow: var(--shadow-sm);
}

.step-card.completed {
  border-color: var(--color-success);
}

.step-number {
  font-size: 0.72rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-subtle);
}

.step-card.active .step-number {
  color: var(--color-primary);
}

.step-card.completed .step-number {
  color: var(--color-success);
}

.step-title {
  font-size: 0.92rem;
  font-weight: 700;
  color: var(--text-main);
  margin-top: 0.15rem;
}

.step-subtitle {
  font-size: 0.75rem;
  color: var(--text-muted);
  line-height: 1.3;
}

/* Active Step Canvas / Stage */
.stage-card {
  background: var(--bg-surface);
  border: 2px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
  box-shadow: var(--shadow-sm);
}

.stage-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1.5px solid var(--border-color);
  padding-bottom: 0.85rem;
}

.stage-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.82rem;
  font-weight: 800;
  padding: 4px 10px;
  border-radius: var(--radius-full);
}

.stage-badge.level-1 { background: #dbeafe; color: #1e40af; border: 1px solid #bfdbfe; }
.stage-badge.level-2 { background: #d1fae5; color: #065f46; border: 1px solid #a7f3d0; }
.stage-badge.level-3 { background: #fef3c7; color: #92400e; border: 1px solid #fde68a; }
.stage-badge.level-4 { background: #ede9fe; color: #5b21b6; border: 1px solid #ddd6fe; }

.stage-title {
  font-size: 1.2rem;
  font-weight: 800;
  color: var(--text-main);
}

.stage-instruction {
  font-size: 0.9rem;
  color: var(--text-muted);
}

/* Quick Select Grid for Steps */
.step-options-grid {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.option-chip {
  background: var(--bg-surface-alt);
  border: 1.5px solid var(--border-color);
  color: var(--text-main);
  padding: 0.45rem 0.85rem;
  border-radius: var(--radius-md);
  font-size: 0.88rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.15s ease;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.option-chip:hover {
  border-color: var(--color-primary);
  background: var(--color-primary-bg);
}

.option-chip.selected {
  background: var(--color-primary);
  color: var(--text-inverse);
  border-color: var(--color-primary);
}

/* Form Controls in Step 2 */
.grammar-controls-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1rem;
}

.form-group {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}

.form-label {
  font-size: 0.82rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.03em;
  color: var(--text-muted);
}

.form-select, .form-input {
  padding: 0.55rem 0.75rem;
  border: 1.5px solid var(--border-color);
  border-radius: var(--radius-sm);
  background: var(--bg-app);
  color: var(--text-main);
  font-size: 0.9rem;
  font-family: inherit;
  outline: none;
}

.form-select:focus, .form-input:focus {
  border-color: var(--border-focus);
}

/* Live Sentence Construction Board */
.sentence-board {
  background: var(--bg-surface);
  border: 2px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 1.25rem 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
  box-shadow: var(--shadow-md);
}

.board-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.board-title {
  font-size: 0.88rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.sentence-editor-area {
  width: 100%;
  font-size: 1.25rem;
  font-weight: 600;
  line-height: 1.6;
  color: var(--text-main);
  background: var(--bg-app);
  border: 2px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1rem;
  min-height: 90px;
  resize: vertical;
  outline: none;
  font-family: inherit;
  transition: border-color 0.15s;
}

.sentence-editor-area:focus {
  border-color: var(--border-focus);
}

.board-tools-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.board-hints {
  font-size: 0.8rem;
  color: var(--text-subtle);
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

/* AI Suggestions & Feedback Panel */
.ai-results-box {
  background: var(--bg-surface);
  border: 2px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 1.25rem 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.ai-header-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.ai-header-title {
  font-size: 1rem;
  font-weight: 800;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--text-main);
}

.ai-suggestion-card {
  background: var(--bg-app);
  border: 1.5px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1rem;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  transition: all 0.15s ease;
}

.ai-suggestion-card:hover {
  border-color: var(--color-primary);
}

.ai-suggestion-text {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text-main);
}

.ai-suggestion-translation {
  font-size: 0.88rem;
  color: var(--text-muted);
  font-style: italic;
}

.ai-suggestion-meta {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-top: 0.25rem;
  padding-top: 0.5rem;
  border-top: 1px dashed var(--border-color);
}

.ai-suggestion-explanation {
  font-size: 0.82rem;
  color: var(--text-subtle);
  flex: 1;
}

/* Grammar Verdict Card */
.grammar-verdict-card {
  padding: 1rem;
  border-radius: var(--radius-md);
  border: 2px solid;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.grammar-verdict-card.adequate {
  background: var(--color-success-bg);
  border-color: var(--color-success-border);
  color: var(--text-main);
}

.grammar-verdict-card.inadequate {
  background: var(--color-warning-bg);
  border-color: var(--color-warning-border);
  color: var(--text-main);
}

.verdict-header {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-weight: 800;
  font-size: 1rem;
}

.verdict-header.adequate { color: var(--color-success); }
.verdict-header.inadequate { color: var(--color-warning); }

.verdict-body {
  font-size: 0.9rem;
  line-height: 1.5;
}

.verdict-alternatives {
  margin-top: 0.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.verdict-alt-item {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  padding: 0.65rem 0.85rem;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
}

/* Action Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.45rem;
  padding: 0.55rem 1rem;
  border-radius: var(--radius-md);
  font-weight: 700;
  font-size: 0.88rem;
  cursor: pointer;
  transition: all 0.15s ease;
  border: 1.5px solid transparent;
  font-family: inherit;
  text-decoration: none;
  white-space: nowrap;
}

.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.btn-primary {
  background: var(--color-primary);
  color: var(--text-inverse);
}

.btn-primary:hover:not(:disabled) {
  background: var(--color-primary-hover);
}

.btn-secondary {
  background: var(--bg-surface-alt);
  border-color: var(--border-color);
  color: var(--text-main);
}

.btn-secondary:hover:not(:disabled) {
  border-color: var(--text-main);
  background: var(--bg-surface);
}

.btn-ai {
  background: linear-gradient(135deg, #4f46e5 0%, #7c3aed 100%);
  color: #ffffff;
  border: none;
}

.btn-ai:hover:not(:disabled) {
  filter: brightness(1.1);
}

.btn-success {
  background: var(--color-success);
  color: #ffffff;
}

.btn-success:hover:not(:disabled) {
  filter: brightness(1.1);
}

.btn-sm {
  padding: 0.35rem 0.65rem;
  font-size: 0.8rem;
  border-radius: var(--radius-sm);
}

.btn-icon-only {
  width: 36px;
  height: 36px;
  padding: 0;
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.1rem;
}

/* Mobile-only sidebar drawer toggle (must come after .btn to win) */
.sidebar-mobile-toggle {
  display: none;
}

/* Footer / Navigation Bar */
.builder-nav-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding-top: 1rem;
  border-top: 2px solid var(--border-color);
  margin-top: 0.5rem;
}

/* Modals */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.65);
  backdrop-filter: blur(2px);
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1.5rem;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.2s ease;
}

.modal-overlay.open {
  opacity: 1;
  pointer-events: auto;
}

.modal-content {
  background: var(--bg-surface);
  border: 2px solid var(--border-color);
  border-radius: var(--radius-lg);
  max-width: 640px;
  width: 100%;
  max-height: 85vh;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  box-shadow: var(--shadow-lg);
  transform: translateY(10px);
  transition: transform 0.2s ease;
}

.modal-overlay.open .modal-content {
  transform: translateY(0);
}

.modal-header {
  padding: 1rem 1.25rem;
  border-bottom: 1.5px solid var(--border-color);
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: var(--bg-surface-alt);
}

.modal-title {
  font-size: 1.1rem;
  font-weight: 800;
  color: var(--text-main);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.modal-close {
  background: transparent;
  border: none;
  font-size: 1.3rem;
  color: var(--text-subtle);
  cursor: pointer;
  padding: 4px;
  line-height: 1;
}

.modal-close:hover {
  color: var(--text-main);
}

.modal-body {
  padding: 1.25rem;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.modal-footer {
  padding: 0.85rem 1.25rem;
  border-top: 1.5px solid var(--border-color);
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: 0.5rem;
  background: var(--bg-surface-alt);
}

/* Topics Grid Modal */
.topics-picker-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(180px, 1fr));
  gap: 0.75rem;
}

.topic-card-item {
  border: 2px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 0.85rem;
  cursor: pointer;
  background: var(--bg-app);
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
  transition: all 0.15s ease;
}

.topic-card-item:hover {
  border-color: var(--color-primary);
  background: var(--color-primary-bg);
}

.topic-card-item.selected {
  border-color: var(--color-primary);
  background: var(--color-primary-bg);
  box-shadow: 0 0 0 2px var(--color-primary);
}

.topic-card-top {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.topic-card-icon {
  font-size: 1.5rem;
}

.topic-card-name {
  font-weight: 800;
  font-size: 0.95rem;
  color: var(--text-main);
}

.topic-card-desc {
  font-size: 0.78rem;
  color: var(--text-muted);
  line-height: 1.3;
}

/* Library Modal List */
.library-search-bar {
  display: flex;
  gap: 0.5rem;
  margin-bottom: 0.5rem;
}

.library-items-list {
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
  max-height: 55vh;
  overflow-y: auto;
}

.library-card {
  border: 1.5px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1rem;
  background: var(--bg-app);
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.library-sentence {
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text-main);
  line-height: 1.4;
}

.library-meta-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.5rem;
  font-size: 0.78rem;
  color: var(--text-subtle);
  border-top: 1px dashed var(--border-color);
  padding-top: 0.5rem;
}

.library-actions {
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

/* Spinner */
.spinner {
  width: 18px;
  height: 18px;
  border: 2px solid rgba(255, 255, 255, 0.4);
  border-top-color: #ffffff;
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
  display: inline-block;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

/* Notification Toast */
.toast-container {
  position: fixed;
  bottom: 1.5rem;
  right: 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  z-index: 200;
  pointer-events: none;
}

.toast {
  background: var(--text-main);
  color: var(--text-inverse);
  padding: 0.75rem 1.25rem;
  border-radius: var(--radius-md);
  font-weight: 600;
  font-size: 0.88rem;
  box-shadow: var(--shadow-lg);
  pointer-events: auto;
  opacity: 0;
  transform: translateY(10px);
  transition: all 0.2s ease;
}

.toast.show {
  opacity: 1;
  transform: translateY(0);
}

.toast.success { background: var(--color-success); }
.toast.error { background: var(--color-danger); }
.toast.info { background: var(--color-primary); }

/* ==========================================================================
   MOBILE: sidebar becomes a bounded, collapsible drawer so the builder
   stays visible instead of being pushed off screen.
   ========================================================================== */
@media (max-width: 860px) {
  .sidebar {
    position: static;
    height: auto;
    overflow: visible;
    border-right: none;
    border-bottom: 2px solid var(--border-color);
  }

  .sidebar-mobile-toggle {
    display: inline-flex;
  }

  .vocab-tree {
    flex: none;
    max-height: 60vh;
  }

  /* 4 columns are too narrow: use a 2x2 grid */
  .stepper-nav {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .builder-nav-footer {
    flex-wrap: wrap;
    justify-content: center;
  }

  /* Buttons and inline flex groups may shrink/wrap instead of overflowing */
  .btn {
    white-space: normal;
    text-align: center;
  }

  .board-header > div,
  .board-tools-row > div,
  .builder-nav-footer > div {
    flex-wrap: wrap;
  }

  .library-search-bar .form-input {
    min-width: 0;
  }

  .sidebar.is-collapsed .search-input-wrap,
  .sidebar.is-collapsed .freq-filter-bar,
  .sidebar.is-collapsed .sidebar-tree-controls,
  .sidebar.is-collapsed .vocab-tree {
    display: none;
  }

  .sidebar.is-collapsed .sidebar-header {
    border-bottom: none;
    gap: 0;
  }
}