/* ==========================================================================
   Math Worksheet Generator — Visual Reskin
   Cascades over style.css. Warm orange on cream, glassmorphic cards,
   Nunito Sans, animated breathing background. No @media print rules —
   print behavior is owned by style.css and must stay unchanged.
   ========================================================================== */

html, body { height: 100%; }

body {
  font-family: var(--font-sans);
  color: var(--fg-primary);
  background: #fffaf4;
  line-height: 1.5;
  min-height: 100vh;
  position: relative;
  overflow-x: hidden;
}

/* Breathing background gradient */
body::before {
  content: "";
  position: fixed;
  inset: 0;
  z-index: -1;
  background:
    radial-gradient(circle at 10% 8%, rgba(239, 134, 57, 0.22), transparent 38%),
    radial-gradient(circle at 88% 18%, rgba(245, 158, 68, 0.18), transparent 42%),
    radial-gradient(circle at 50% 92%, rgba(255, 212, 154, 0.22), transparent 45%),
    linear-gradient(160deg, #fffaf4 0%, #ffeed6 48%, #ffe3bf 100%);
  animation: skin-breathe 25s cubic-bezier(0.4, 0, 0.2, 1) infinite;
}

@keyframes skin-breathe {
  0%, 100% { transform: scale(1); opacity: 1; }
  50%      { transform: scale(1.06); opacity: 0.92; }
}

@media (prefers-reduced-motion: reduce) {
  body::before { animation: none; }
}

/* ==========================================================================
   Header
   ========================================================================== */

body > header {
  background: linear-gradient(140deg,
    rgba(108, 41, 13, 0.9) 0%,
    rgba(163, 63, 17, 0.92) 52%,
    rgba(216, 100, 36, 0.9) 100%);
  backdrop-filter: blur(16px);
  box-shadow: var(--shadow-header);
  padding: var(--space-4) var(--space-8);
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: var(--space-6);
  border-bottom: 1px solid rgba(255, 255, 255, 0.18);
  margin-bottom: 0;
  animation: skin-header-slide-in 0.45s cubic-bezier(0.4, 0, 0.2, 1);
}

@keyframes skin-header-slide-in {
  from { transform: translateY(-12px); opacity: 0; }
  to   { transform: translateY(0);     opacity: 1; }
}

.header-brand {
  display: flex;
  align-items: center;
  gap: var(--space-3);
}

.brand-mark {
  width: 36px;
  height: 36px;
  border-radius: var(--radius-md);
  background: linear-gradient(145deg, #fff8f0, #ffe3bf);
  color: var(--color-orange-dark);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: var(--weight-bold);
  font-size: 1.15rem;
  box-shadow: 0 4px 10px rgba(73, 27, 8, 0.3);
  letter-spacing: -0.02em;
  flex-shrink: 0;
}

body > header h1 {
  font-size: var(--text-xl);
  font-weight: var(--weight-bold);
  color: #fff8f0;
  letter-spacing: -0.01em;
  line-height: 1.1;
  margin: 0;
  text-align: left;
  flex-grow: 0;
}

.header-brand .tagline {
  font-size: var(--text-xs);
  font-weight: var(--weight-semibold);
  color: rgba(255, 243, 226, 0.78);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-top: 2px;
}

/* ==========================================================================
   Language switcher (pill)
   ========================================================================== */

#language-switcher {
  display: flex;
  gap: var(--space-2);
  background: rgba(255, 255, 255, 0.1);
  border: 1px solid rgba(255, 255, 255, 0.2);
  border-radius: var(--radius-full);
  padding: 4px;
  font-size: 18px;
}

#language-switcher .language-flag {
  cursor: pointer;
  font-size: 18px;
  width: 32px;
  height: 32px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-full);
  transition: all var(--transition-fast);
  filter: drop-shadow(0 0 1px rgba(0, 0, 0, 0.2));
  padding: 0;
}

#language-switcher .language-flag:hover {
  background: rgba(255, 255, 255, 0.16);
  transform: scale(1.08);
  filter: drop-shadow(0 0 1px rgba(0, 0, 0, 0.2));
}

#language-switcher .language-flag.active {
  background: rgba(255, 248, 240, 0.95);
  box-shadow: 0 2px 8px rgba(73, 27, 8, 0.3);
}

/* ==========================================================================
   App shell
   ========================================================================== */

.app-container {
  display: flex;
  align-items: flex-start;
  max-width: 1400px;
  margin: var(--space-6) auto;
  padding: 0 var(--space-6);
  gap: var(--space-6);
  min-height: calc(100vh - 200px);
  background: transparent;
  animation: skin-rise-in 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}

@keyframes skin-rise-in {
  from { transform: translateY(14px); opacity: 0; }
  to   { transform: translateY(0);    opacity: 1; }
}

main {
  flex: 1;
  min-width: 0;
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
  padding: 0;
}

/* ==========================================================================
   Topic sidebar
   ========================================================================== */

.topic-sidebar {
  width: 290px;
  flex-shrink: 0;
  background: rgba(255, 252, 247, 0.88);
  backdrop-filter: blur(18px);
  border: 1px solid rgba(255, 255, 255, 0.65);
  border-right: 1px solid rgba(255, 255, 255, 0.65);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-card);
  padding: var(--space-6) var(--space-4);
  max-height: calc(100vh - 140px);
  position: sticky;
  top: var(--space-6);
  overflow-y: auto;
  height: auto;
}

.topic-sidebar h2 {
  font-size: var(--text-xs);
  font-weight: var(--weight-bold);
  color: var(--fg-muted);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin: 0 var(--space-2) var(--space-4);
  padding-bottom: 0;
  border-bottom: none;
}

.topic-tree {
  list-style: none;
  padding: 0;
  margin: 0;
}

.topic-category {
  margin-bottom: var(--space-2);
}

.category-header {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  padding: 10px 12px;
  cursor: pointer;
  border-radius: var(--radius-md);
  background: transparent;
  transition: background var(--transition-fast), color var(--transition-fast);
  user-select: none;
}

.category-header:hover {
  background: linear-gradient(90deg, #fff2dc, #ffe3bf);
}

.category-toggle {
  display: inline-flex;
  width: 14px;
  height: 14px;
  align-items: center;
  justify-content: center;
  color: var(--color-orange-dark);
  font-size: 10px;
  transition: transform var(--transition-fast);
  flex-shrink: 0;
}

.topic-category.expanded .category-toggle {
  transform: rotate(90deg);
}

.category-name {
  font-weight: var(--weight-semibold);
  color: var(--fg-primary);
  font-size: var(--text-sm);
}

.topic-category.expanded .category-header {
  background: linear-gradient(90deg, rgba(255, 242, 220, 0.8), rgba(255, 227, 191, 0.4));
}

.topic-list {
  list-style: none;
  padding: var(--space-1) 0 var(--space-2) 26px;
  margin: 0;
  max-height: 0;
  overflow: hidden;
  opacity: 0;
  transition: max-height var(--transition-slow), opacity var(--transition-base);
}

.topic-category.expanded .topic-list {
  max-height: 600px;
  opacity: 1;
}

.topic-item {
  padding: 8px 12px;
  cursor: pointer;
  font-size: var(--text-sm);
  color: var(--fg-secondary);
  border-radius: var(--radius-sm);
  border-left: 3px solid transparent;
  margin-left: -12px;
  padding-left: 15px;
  transition: all var(--transition-fast);
  display: flex;
  align-items: center;
  gap: var(--space-2);
  background: transparent;
}

.topic-item:hover {
  background: rgba(255, 242, 220, 0.6);
  border-left-color: var(--color-orange-light);
  color: var(--fg-primary);
  padding-left: 18px;
}

.topic-item.selected {
  background: linear-gradient(90deg, rgba(239, 134, 57, 0.16), rgba(255, 227, 191, 0.4));
  border-left-color: var(--color-orange);
  color: var(--color-orange-dark);
  font-weight: var(--weight-semibold);
}

/* ==========================================================================
   Main panel
   ========================================================================== */

.panel {
  background: rgba(255, 252, 247, 0.88);
  backdrop-filter: blur(18px);
  border: 1px solid rgba(255, 255, 255, 0.65);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-card);
  padding: var(--space-6);
}

.panel-title {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  font-size: var(--text-xs);
  font-weight: var(--weight-bold);
  color: var(--fg-muted);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-bottom: var(--space-4);
}

.panel-title::after {
  content: "";
  flex: 1;
  height: 1px;
  background: linear-gradient(to right, rgba(163, 63, 17, 0.18), transparent);
}

.panel-title .topic-badge {
  margin-left: auto;
  font-size: var(--text-sm);
  font-weight: var(--weight-bold);
  color: var(--color-orange-dark);
  text-transform: none;
  letter-spacing: 0;
  padding: 4px 12px;
  background: rgba(239, 134, 57, 0.12);
  border-radius: var(--radius-full);
  white-space: nowrap;
}

/* ==========================================================================
   Controls
   ========================================================================== */

#controls-panel.controls h2 { display: none; } /* hidden in favor of .panel-title */

#controls-panel .control-group label {
  display: block;
  font-size: var(--text-xs);
  font-weight: var(--weight-bold);
  color: var(--fg-muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-bottom: 6px;
}

#controls-panel .control-group input[type="number"],
#controls-panel .control-group input[type="text"],
#controls-panel .control-group select {
  width: 100%;
  padding: 10px 12px;
  border: 2px solid rgba(163, 63, 17, 0.18);
  border-radius: var(--radius-md);
  background: rgba(255, 250, 243, 0.95);
  backdrop-filter: blur(4px);
  font-family: inherit;
  font-size: var(--text-base);
  font-weight: var(--weight-semibold);
  color: var(--fg-primary);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

#controls-panel .control-group input[type="number"]:focus,
#controls-panel .control-group input[type="text"]:focus,
#controls-panel .control-group select:focus {
  outline: none;
  border-color: var(--color-orange);
  box-shadow: 0 0 0 3px var(--color-focus);
}

/* ==========================================================================
   Actions
   ========================================================================== */

#actions-panel {
  display: flex;
  gap: var(--space-3);
  flex-wrap: wrap;
  padding: 0;
  margin: 0;
}

.button {
  font-family: inherit;
  font-size: var(--text-base);
  font-weight: var(--weight-bold);
  padding: 12px 24px;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-base);
  border: none;
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  text-transform: none;
  letter-spacing: 0;
}

.button-primary {
  background: linear-gradient(145deg, #a33f11, #d86424, #ef8639);
  color: #fff8f0;
  box-shadow: var(--shadow-btn);
  border: 1px solid rgba(255, 244, 234, 0.15);
}

.button-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 12px 24px rgba(105, 45, 18, 0.32);
  background: linear-gradient(145deg, #a33f11, #d86424, #ef8639);
}

.button-primary:active { transform: scale(0.97); }

.button-secondary {
  background: linear-gradient(145deg, #fff9f0, #ffeacc);
  color: var(--color-orange-dark);
  border: 1px solid rgba(163, 63, 17, 0.2);
  box-shadow: 0 4px 10px rgba(105, 45, 18, 0.1);
}

.button-secondary:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 18px rgba(105, 45, 18, 0.18);
  background: linear-gradient(145deg, #fff9f0, #ffeacc);
}

.button-secondary:active { transform: scale(0.97); }

.hotkey {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 22px;
  padding: 2px 6px;
  background: rgba(255, 255, 255, 0.22);
  border: 1px solid rgba(255, 255, 255, 0.4);
  border-radius: var(--radius-sm);
  font-size: 11px;
  font-weight: var(--weight-bold);
  letter-spacing: 0.04em;
  font-family: var(--font-mono);
}

.button-secondary .hotkey {
  background: rgba(163, 63, 17, 0.08);
  border-color: rgba(163, 63, 17, 0.2);
  color: var(--color-orange-dark);
}

/* ==========================================================================
   Problems output
   ========================================================================== */

#output-area.problems {
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
}

#output-area.problems > h2 { display: none; }

.problems-empty {
  text-align: center;
  padding: var(--space-16) var(--space-8);
  color: var(--fg-muted);
}

.problems-empty .proverb {
  font-size: var(--text-lg);
  font-weight: var(--weight-bold);
  font-style: italic;
  color: var(--color-orange-dark);
  margin-bottom: var(--space-2);
}

.problems-empty .proverb-en {
  font-size: var(--text-sm);
  color: var(--fg-secondary);
  margin-bottom: var(--space-6);
}

.problems-empty .hint-text {
  font-size: var(--text-base);
  color: var(--fg-secondary);
}

/* ==========================================================================
   Footer
   ========================================================================== */

body > footer {
  text-align: center;
  padding: var(--space-6) var(--space-4) var(--space-8);
  font-size: var(--text-xs);
  color: var(--fg-muted);
  background: transparent;
  border-top: none;
}

body > footer #commit-sha {
  font-family: var(--font-mono);
  color: var(--color-orange-dark);
}

/* ==========================================================================
   Responsive
   ========================================================================== */

@media (max-width: 960px) {
  .app-container {
    flex-direction: column;
    padding: 0 var(--space-4);
  }
  .topic-sidebar {
    width: 100%;
    position: static;
    max-height: none;
  }
}