/* ============================================================
   ALGEBRA WEBAPP — STYLES
   Modern educational theme with purple/blue palette
   ============================================================ */

/* --- CSS Custom Properties --- */
:root {
  /* Primary palette */
  --color-primary: #6c5ce7;
  --color-primary-light: #a29bfe;
  --color-primary-dark: #4834d4;
  --color-primary-bg: #f0edff;

  /* Accent */
  --color-accent: #00b894;
  --color-accent-light: #55efc4;
  --color-accent-dark: #00a884;

  /* Semantic colors */
  --color-success: #00b894;
  --color-warning: #fdcb6e;
  --color-danger: #e17055;
  --color-info: #74b9ff;

  /* Neutrals */
  --color-bg: #f8f9fc;
  --color-surface: #ffffff;
  --color-surface-hover: #f5f3ff;
  --color-border: #e2e0f0;
  --color-text: #2d3436;
  --color-text-secondary: #636e72;
  --color-text-muted: #b2bec3;

  /* Shadows */
  --shadow-sm: 0 1px 3px rgba(108, 92, 231, 0.08);
  --shadow-md: 0 4px 12px rgba(108, 92, 231, 0.12);
  --shadow-lg: 0 8px 30px rgba(108, 92, 231, 0.16);

  /* Radius */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 24px;

  /* Typography */
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;

  /* Spacing */
  --space-xs: 4px;
  --space-sm: 8px;
  --space-md: 16px;
  --space-lg: 24px;
  --space-xl: 32px;
  --space-2xl: 48px;

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-normal: 250ms ease;
  --transition-slow: 400ms ease;

  /* Layout */
  --navbar-height: 60px;
  --max-width: 1200px;
}

/* --- Dark Theme --- */
[data-theme="dark"] {
  --color-bg: #1a1a2e;
  --color-surface: #16213e;
  --color-surface-hover: #1f2b4d;
  --color-border: #2d3a5c;
  --color-text: #e8e8f0;
  --color-text-secondary: #a0a0c0;
  --color-text-muted: #5c5c7a;
  --color-primary-bg: #1f1a3e;
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.2);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 8px 30px rgba(0, 0, 0, 0.4);
}

/* --- Reset & Base --- */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-sans);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

a {
  color: var(--color-primary);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--color-primary-dark);
}

/* --- Navbar --- */
.navbar {
  position: sticky;
  top: 0;
  z-index: 100;
  display: flex;
  align-items: center;
  height: var(--navbar-height);
  padding: 0 var(--space-lg);
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  box-shadow: var(--shadow-sm);
  backdrop-filter: blur(10px);
}

.navbar__brand {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  margin-right: var(--space-xl);
}

.navbar__icon {
  font-size: 1.5rem;
  color: var(--color-primary);
}

.navbar__title {
  font-size: 1.2rem;
  font-weight: 700;
  background: linear-gradient(135deg, var(--color-primary), var(--color-primary-dark));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.navbar__links {
  display: flex;
  gap: var(--space-sm);
  flex: 1;
}

.navbar__link {
  padding: var(--space-sm) var(--space-md);
  border-radius: var(--radius-sm);
  font-weight: 500;
  color: var(--color-text-secondary);
  transition: all var(--transition-fast);
}

.navbar__link:hover {
  background: var(--color-primary-bg);
  color: var(--color-primary);
}

.navbar__link--active {
  background: var(--color-primary);
  color: white !important;
}

.navbar__theme-toggle {
  background: none;
  border: 2px solid var(--color-border);
  border-radius: var(--radius-sm);
  padding: var(--space-sm) var(--space-sm);
  cursor: pointer;
  font-size: 1.1rem;
  color: var(--color-text-secondary);
  transition: all var(--transition-fast);
  display: flex;
  align-items: center;
  justify-content: center;
}

.navbar__theme-toggle:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
}

/* --- App Container --- */
.app-container {
  flex: 1;
  max-width: var(--max-width);
  width: 100%;
  margin: 0 auto;
  padding: var(--space-lg);
}

/* --- Loading Screen --- */
.loading-screen {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 300px;
  gap: var(--space-md);
  color: var(--color-text-muted);
}

.loading-spinner {
  width: 40px;
  height: 40px;
  border: 3px solid var(--color-border);
  border-top-color: var(--color-primary);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

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

/* --- Footer --- */
.footer {
  text-align: center;
  padding: var(--space-lg);
  color: var(--color-text-muted);
  font-size: 0.85rem;
  border-top: 1px solid var(--color-border);
}

/* ============================================================
   HOME PAGE
   ============================================================ */
.home-page {
  text-align: center;
  padding: var(--space-2xl) 0;
}

.home-page__hero {
  margin-bottom: var(--space-2xl);
}

.home-page__hero h1 {
  font-size: 2.5rem;
  font-weight: 800;
  background: linear-gradient(135deg, var(--color-primary), var(--color-accent));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: var(--space-md);
}

.home-page__hero p {
  font-size: 1.1rem;
  color: var(--color-text-secondary);
  max-width: 600px;
  margin: 0 auto;
}

.home-page__cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: var(--space-lg);
  max-width: 900px;
  margin: 0 auto;
}

.home-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  text-align: center;
  cursor: pointer;
  transition: all var(--transition-normal);
  box-shadow: var(--shadow-sm);
}

.home-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
  border-color: var(--color-primary-light);
}

.home-card__icon {
  font-size: 2.5rem;
  margin-bottom: var(--space-md);
}

.home-card__title {
  font-size: 1.2rem;
  font-weight: 700;
  margin-bottom: var(--space-sm);
  color: var(--color-text);
}

.home-card__desc {
  color: var(--color-text-secondary);
  font-size: 0.95rem;
}

/* ============================================================
   EXERCISE BROWSER
   ============================================================ */
.exercise-browser {
  animation: fadeIn 0.3s ease;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: translateY(0); }
}

.exercise-browser__header {
  margin-bottom: var(--space-lg);
}

.exercise-browser__header h2 {
  font-size: 1.8rem;
  font-weight: 700;
  margin-bottom: var(--space-sm);
}

.exercise-browser__header p {
  color: var(--color-text-secondary);
}

.exercise-browser__search {
  width: 100%;
  max-width: 400px;
  padding: var(--space-sm) var(--space-md);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  font-size: 1rem;
  background: var(--color-surface);
  color: var(--color-text);
  transition: border-color var(--transition-fast);
  margin-bottom: var(--space-lg);
}

.exercise-browser__search:focus {
  outline: none;
  border-color: var(--color-primary);
}

.exercise-browser__search::placeholder {
  color: var(--color-text-muted);
}

/* Topic filter tabs */
.topic-tabs {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
  margin-bottom: var(--space-lg);
}

.topic-tab {
  padding: var(--space-sm) var(--space-md);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-xl);
  background: var(--color-surface);
  color: var(--color-text-secondary);
  font-size: 0.9rem;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition-fast);
  display: flex;
  align-items: center;
  gap: var(--space-xs);
}

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

.topic-tab--active {
  background: var(--color-primary);
  color: white;
  border-color: var(--color-primary);
}

.topic-tab__count {
  background: rgba(255, 255, 255, 0.2);
  padding: 1px 8px;
  border-radius: 12px;
  font-size: 0.75rem;
}

.topic-tab--active .topic-tab__count {
  background: rgba(255, 255, 255, 0.25);
}

.topic-tab:not(.topic-tab--active) .topic-tab__count {
  background: var(--color-primary-bg);
  color: var(--color-primary);
}

/* Exercise cards grid */
.exercise-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: var(--space-md);
}

.exercise-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  cursor: pointer;
  transition: all var(--transition-normal);
  box-shadow: var(--shadow-sm);
  position: relative;
  overflow: hidden;
}

.exercise-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 4px;
  height: 100%;
  background: var(--color-primary);
  opacity: 0;
  transition: opacity var(--transition-fast);
}

.exercise-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
  border-color: var(--color-primary-light);
}

.exercise-card:hover::before {
  opacity: 1;
}

.exercise-card__id {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--color-primary);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: var(--space-sm);
}

.exercise-card__topic {
  display: inline-block;
  padding: 2px 10px;
  background: var(--color-primary-bg);
  color: var(--color-primary);
  border-radius: var(--radius-sm);
  font-size: 0.75rem;
  font-weight: 600;
  margin-bottom: var(--space-sm);
}

.exercise-card__statement {
  font-size: 0.95rem;
  color: var(--color-text);
  margin-bottom: var(--space-sm);
  line-height: 1.5;
}

.exercise-card__difficulty {
  font-size: 0.8rem;
  color: var(--color-text-muted);
}

.exercise-browser__empty {
  text-align: center;
  padding: var(--space-2xl);
  color: var(--color-text-muted);
}

.exercise-browser__empty p {
  font-size: 1.1rem;
}

/* ============================================================
   EXERCISE VIEWER
   ============================================================ */
.exercise-viewer {
  animation: fadeIn 0.3s ease;
  max-width: 800px;
  margin: 0 auto;
}

.exercise-viewer__back {
  display: inline-flex;
  align-items: center;
  gap: var(--space-xs);
  color: var(--color-text-secondary);
  font-weight: 500;
  margin-bottom: var(--space-lg);
  cursor: pointer;
  padding: var(--space-sm) var(--space-md);
  border-radius: var(--radius-sm);
  transition: all var(--transition-fast);
  background: none;
  border: none;
  font-size: 0.95rem;
}

.exercise-viewer__back:hover {
  color: var(--color-primary);
  background: var(--color-primary-bg);
}

.exercise-viewer__problem {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  margin-bottom: var(--space-lg);
  box-shadow: var(--shadow-sm);
}

.exercise-viewer__problem-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: var(--space-md);
}

.exercise-viewer__problem-id {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--color-primary);
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.exercise-viewer__problem-topic {
  padding: 4px 12px;
  background: var(--color-primary-bg);
  color: var(--color-primary);
  border-radius: var(--radius-sm);
  font-size: 0.8rem;
  font-weight: 600;
}

.exercise-viewer__statement {
  font-size: 1.1rem;
  line-height: 1.8;
  margin-bottom: var(--space-md);
}

.exercise-viewer__hint {
  padding: var(--space-md);
  background: var(--color-primary-bg);
  border-radius: var(--radius-md);
  color: var(--color-primary-dark);
  font-size: 0.9rem;
  margin-top: var(--space-md);
  display: none;
}

.exercise-viewer__hint--visible {
  display: block;
}

.exercise-viewer__theory-btn {
  margin-top: var(--space-sm);
  padding: var(--space-sm) var(--space-md);
  background: none;
  border: 1px solid var(--color-accent);
  color: var(--color-accent-dark);
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 0.85rem;
  transition: all var(--transition-fast);
}

.exercise-viewer__theory-btn:hover {
  background: #e8f5e9;
}

.exercise-viewer__theory {
  display: none;
  margin-top: var(--space-md);
  padding: var(--space-lg);
  background: var(--color-primary-bg);
  border-radius: var(--radius-md);
  border: 1px solid var(--color-primary-light);
}

.exercise-viewer__theory--visible {
  display: block;
}

.theory-panel h4 {
  font-size: 1.1rem;
  color: var(--color-primary);
  margin-bottom: var(--space-md);
}

.theory-content {
  font-size: 0.95rem;
  line-height: 1.7;
  color: var(--color-text);
}

.theory-panel .katex {
  font-size: 1em;
}

.exercise-viewer__hint-btn {
  margin-top: var(--space-sm);
  padding: var(--space-sm) var(--space-md);
  background: none;
  border: 1px solid var(--color-warning);
  color: #d68910;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 0.85rem;
  transition: all var(--transition-fast);
}

.exercise-viewer__hint-btn:hover {
  background: #fef9e7;
}

/* Attempt area */
.exercise-viewer__attempt {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  margin-bottom: var(--space-lg);
  box-shadow: var(--shadow-sm);
}

.exercise-viewer__attempt h3 {
  font-size: 1.1rem;
  margin-bottom: var(--space-md);
  color: var(--color-text-secondary);
}

.attempt-input {
  display: flex;
  gap: var(--space-sm);
  align-items: center;
}

.attempt-input__field {
  flex: 1;
  padding: var(--space-sm) var(--space-md);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-sm);
  font-size: 1rem;
  font-family: var(--font-mono);
  background: var(--color-bg);
  color: var(--color-text);
  transition: border-color var(--transition-fast);
}

.attempt-input__field:focus {
  outline: none;
  border-color: var(--color-primary);
}

.attempt-input__submit {
  padding: var(--space-sm) var(--space-lg);
  background: var(--color-primary);
  color: white;
  border: none;
  border-radius: var(--radius-sm);
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.attempt-input__submit:hover {
  background: var(--color-primary-dark);
}

.attempt-feedback {
  margin-top: var(--space-md);
  padding: var(--space-md);
  border-radius: var(--radius-sm);
  font-weight: 500;
  display: none;
}

.attempt-feedback--correct {
  display: block;
  background: #d5f5e3;
  color: #1e8449;
  border: 1px solid #82e0aa;
}

.attempt-feedback--incorrect {
  display: block;
  background: #fadbd8;
  color: #c0392b;
  border: 1px solid #f1948a;
}

[data-theme="dark"] .attempt-feedback--correct {
  background: #1a3a2a;
  border-color: #2d6a4f;
}

[data-theme="dark"] .attempt-feedback--incorrect {
  background: #3a1a1a;
  border-color: #6a2d2d;
}

/* Solution steps */
.exercise-viewer__solution {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  box-shadow: var(--shadow-sm);
}

.exercise-viewer__solution h3 {
  font-size: 1.2rem;
  margin-bottom: var(--space-lg);
  color: var(--color-primary);
}

.solution-steps {
  list-style: none;
  counter-reset: step;
}

.solution-step {
  counter-increment: step;
  position: relative;
  padding: var(--space-md);
  padding-left: var(--space-xl);
  margin-bottom: var(--space-md);
  background: var(--color-bg);
  border-radius: var(--radius-md);
  border-left: 3px solid var(--color-primary-light);
  animation: fadeIn 0.3s ease;
  overflow-x: auto;
}

.solution-step::before {
  content: counter(step);
  position: absolute;
  left: 8px;
  top: var(--space-md);
  width: 24px;
  height: 24px;
  background: var(--color-primary);
  color: white;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.75rem;
  font-weight: 700;
}

.solution-step__desc {
  font-size: 0.95rem;
  color: var(--color-text-secondary);
  margin-bottom: var(--space-sm);
}

.solution-step__expression {
  font-size: 1.05rem;
}

.reveal-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  width: 100%;
  padding: var(--space-md);
  background: var(--color-primary-bg);
  color: var(--color-primary);
  border: 2px dashed var(--color-primary-light);
  border-radius: var(--radius-md);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition-fast);
  margin-top: var(--space-md);
}

.reveal-btn:hover {
  background: var(--color-primary);
  color: white;
  border-style: solid;
}

.solution-answer {
  margin-top: var(--space-lg);
  padding: var(--space-lg);
  background: linear-gradient(135deg, var(--color-primary-bg), #e8f5e9);
  border-radius: var(--radius-md);
  text-align: center;
  font-size: 1.1rem;
  display: none;
}

[data-theme="dark"] .solution-answer {
  background: linear-gradient(135deg, #1f1a3e, #1a3a2a);
}

.solution-answer--visible {
  display: block;
}

.solution-answer__label {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-primary);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: var(--space-sm);
}

/* ============================================================
   WORKSPACE — MATRIX BUILDER + SYSTEM SOLVER
   ============================================================ */
.workspace {
  animation: fadeIn 0.3s ease;
}

.workspace__header {
  margin-bottom: var(--space-lg);
}

.workspace__header h2 {
  font-size: 1.8rem;
  font-weight: 700;
  margin-bottom: var(--space-sm);
}

.workspace__tabs {
  display: flex;
  gap: var(--space-sm);
  margin-bottom: var(--space-lg);
}

.workspace__tab {
  padding: var(--space-sm) var(--space-lg);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  color: var(--color-text-secondary);
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.workspace__tab:hover {
  border-color: var(--color-primary-light);
  color: var(--color-primary);
}

.workspace__tab--active {
  background: var(--color-primary);
  color: white;
  border-color: var(--color-primary);
}

.workspace__content {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  box-shadow: var(--shadow-sm);
}

/* Matrix Builder */
.matrix-builder {
  max-width: 800px;
}

.matrix-builder__controls {
  display: flex;
  gap: var(--space-md);
  align-items: center;
  margin-bottom: var(--space-lg);
  flex-wrap: wrap;
}

.matrix-builder__size-select {
  padding: var(--space-sm) var(--space-md);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-bg);
  color: var(--color-text);
  font-size: 0.95rem;
  cursor: pointer;
}

.matrix-builder__size-select:focus {
  outline: none;
  border-color: var(--color-primary);
}

/* Matrix grid input */
.matrix-grid {
  display: inline-grid;
  gap: 4px;
  padding: var(--space-md);
  background: var(--color-bg);
  border-radius: var(--radius-md);
  border: 2px solid var(--color-border);
  margin-bottom: var(--space-lg);
  position: relative;
}

/* Bracket decorations */
.matrix-grid::before,
.matrix-grid::after {
  content: '';
  position: absolute;
  top: 8px;
  bottom: 8px;
  width: 8px;
  border: 2px solid var(--color-primary);
}

.matrix-grid::before {
  left: 4px;
  border-right: none;
  border-radius: 4px 0 0 4px;
}

.matrix-grid::after {
  right: 4px;
  border-left: none;
  border-radius: 0 4px 4px 0;
}

.matrix-grid__cell {
  width: 60px;
  height: 40px;
  text-align: center;
  font-size: 1rem;
  font-family: var(--font-mono);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  color: var(--color-text);
  transition: border-color var(--transition-fast);
}

.matrix-grid__cell:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 2px var(--color-primary-bg);
}

.matrix-grid__cell--error {
  border-color: var(--color-danger);
  background: #fef0ee;
}

/* Operation buttons */
.matrix-ops {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
  margin-bottom: var(--space-lg);
}

.matrix-ops__btn {
  padding: var(--space-sm) var(--space-md);
  background: var(--color-primary-bg);
  color: var(--color-primary);
  border: 1px solid var(--color-primary-light);
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.matrix-ops__btn:hover {
  background: var(--color-primary);
  color: white;
}

/* Results display */
.matrix-result {
  margin-top: var(--space-lg);
  padding: var(--space-lg);
  background: var(--color-bg);
  border-radius: var(--radius-md);
  border: 1px solid var(--color-border);
  display: none;
}

.matrix-result--visible {
  display: block;
}

.matrix-result__title {
  font-size: 1rem;
  font-weight: 700;
  color: var(--color-primary);
  margin-bottom: var(--space-md);
}

.matrix-result__value {
  font-size: 1.2rem;
  margin-bottom: var(--space-md);
}

.matrix-result__steps {
  list-style: none;
}

.matrix-result__step {
  padding: var(--space-sm) var(--space-md);
  margin-bottom: var(--space-sm);
  background: var(--color-surface);
  border-radius: var(--radius-sm);
  border-left: 3px solid var(--color-primary-light);
  font-size: 0.9rem;
  overflow-x: auto;
}

/* ============================================================
   SYSTEM SOLVER
   ============================================================ */
.system-solver {
  max-width: 900px;
}

.system-solver__controls {
  display: flex;
  gap: var(--space-md);
  align-items: center;
  margin-bottom: var(--space-lg);
  flex-wrap: wrap;
}

.system-solver__size-select,
.system-solver__method-select {
  padding: var(--space-sm) var(--space-md);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-bg);
  color: var(--color-text);
  font-size: 0.95rem;
  cursor: pointer;
}

.system-solver__size-select:focus,
.system-solver__method-select:focus {
  outline: none;
  border-color: var(--color-primary);
}

.system-solver__matrix-label {
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  margin-bottom: var(--space-sm);
}

/* Augmented matrix grid */
.augmented-grid {
  display: inline-grid;
  gap: 4px;
  padding: var(--space-md);
  background: var(--color-bg);
  border-radius: var(--radius-md);
  border: 2px solid var(--color-border);
  margin-bottom: var(--space-lg);
  position: relative;
}

.augmented-grid__divider {
  width: 2px;
  background: var(--color-primary);
  margin: 0 4px;
}

.system-solver__solve-btn {
  padding: var(--space-sm) var(--space-xl);
  background: var(--color-accent);
  color: white;
  border: none;
  border-radius: var(--radius-sm);
  font-size: 1rem;
  font-weight: 700;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.system-solver__solve-btn:hover {
  background: var(--color-accent-dark);
}

/* Error display */
.error-message {
  padding: var(--space-md);
  background: #fadbd8;
  color: #c0392b;
  border: 1px solid #f1948a;
  border-radius: var(--radius-sm);
  margin-bottom: var(--space-md);
  display: none;
}

.error-message--visible {
  display: block;
}

[data-theme="dark"] .error-message {
  background: #3a1a1a;
  border-color: #6a2d2d;
  color: #f1948a;
}

/* ============================================================
   KATEX OVERRIDES
   ============================================================ */
.katex-display {
  margin: var(--space-md) 0 !important;
  overflow-x: auto;
  overflow-y: hidden;
  padding: var(--space-sm) 0;
}

.katex {
  font-size: 1.05em !important;
}

/* ============================================================
   RESPONSIVE
   ============================================================ */
@media (max-width: 768px) {
  .navbar {
    padding: 0 var(--space-md);
  }

  .navbar__links {
    gap: 2px;
  }

  .navbar__link {
    padding: var(--space-xs) var(--space-sm);
    font-size: 0.85rem;
  }

  .app-container {
    padding: var(--space-md);
  }

  .home-page__hero h1 {
    font-size: 1.8rem;
  }

  .exercise-grid {
    grid-template-columns: 1fr;
  }

  .matrix-grid__cell {
    width: 48px;
    height: 36px;
    font-size: 0.9rem;
  }

  .workspace__tabs {
    flex-wrap: wrap;
  }
}

@media (max-width: 480px) {
  .navbar__brand {
    margin-right: var(--space-sm);
  }

  .navbar__title {
    display: none;
  }

  .home-page__hero h1 {
    font-size: 1.5rem;
  }

  .matrix-grid__cell {
    width: 40px;
    height: 32px;
    font-size: 0.8rem;
  }

  .attempt-input {
    flex-direction: column;
  }

  .attempt-input__submit {
    width: 100%;
  }
}

/* ============================================================
   UTILITY CLASSES
   ============================================================ */
.hidden {
  display: none !important;
}

.text-center {
  text-align: center;
}

.mt-md {
  margin-top: var(--space-md);
}

.mb-md {
  margin-bottom: var(--space-md);
}

/* Scrollbar styling */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

::-webkit-scrollbar-track {
  background: var(--color-bg);
}

::-webkit-scrollbar-thumb {
  background: var(--color-border);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--color-text-muted);
}

/* ============================================================
   PHASE 3: VISUAL EFFECTS
   ============================================================ */

/* --- Glassmorphism --- */
@supports (backdrop-filter: blur(16px)) {
  .exercise-card,
  .matrix-builder,
  .system-solver,
  .navbar,
  .solution-panel,
  .exercise-viewer__problem,
  .exercise-viewer__attempt,
  .exercise-viewer__solution {
    backdrop-filter: blur(16px);
    background: rgba(255, 255, 255, 0.08);
    border: 1px solid rgba(255, 255, 255, 0.12);
  }

  [data-theme="dark"] .exercise-card,
  [data-theme="dark"] .matrix-builder,
  [data-theme="dark"] .system-solver,
  [data-theme="dark"] .navbar,
  [data-theme="dark"] .solution-panel,
  [data-theme="dark"] .exercise-viewer__problem,
  [data-theme="dark"] .exercise-viewer__attempt,
  [data-theme="dark"] .exercise-viewer__solution {
    background: rgba(0, 0, 0, 0.15);
    border: 1px solid rgba(255, 255, 255, 0.08);
  }
}

.glass-card {
  backdrop-filter: blur(16px);
  background: rgba(255, 255, 255, 0.08);
  border: 1px solid rgba(255, 255, 255, 0.12);
  border-radius: 16px;
}

[data-theme="dark"] .glass-card {
  background: rgba(0, 0, 0, 0.15);
}

/* --- Scroll-reveal animations --- */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes fadeInScale {
  from {
    opacity: 0;
    transform: scale(0.95);
  }
  to {
    opacity: 1;
    transform: scale(1);
  }
}

.reveal {
  animation: fadeInUp 0.4s ease forwards;
}

.reveal-scale {
  animation: fadeInScale 0.3s ease forwards;
}

@media (prefers-reduced-motion: reduce) {
  .reveal,
  .reveal-scale {
    animation: none;
    opacity: 1;
    transform: none;
  }
}

/* --- Micro-interactions --- */
button,
.matrix-ops__btn,
.topic-tab,
.navbar__link,
.home-card,
.exercise-card,
.attempt-input__submit {
  transition: all 0.2s ease;
}

button:hover,
.matrix-ops__btn:hover,
.topic-tab:hover,
.navbar__link:hover,
.home-card:hover,
.exercise-card:hover {
  transform: scale(1.03);
  box-shadow: var(--shadow-md);
}

.exercise-card:hover {
  transform: translateY(-2px);
}

:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

.attempt-input__field:focus {
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(108, 92, 231, 0.15);
  outline: none;
}

/* --- Page transitions --- */
.page-enter {
  opacity: 0;
  transform: translateY(8px);
}

.page-enter-active {
  opacity: 1;
  transform: translateY(0);
  transition: opacity 300ms ease, transform 300ms ease;
}

/* ============================================================
   PARTICLES CANVAS BACKGROUND
   ============================================================ */
#particles-bg {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: -1;
  pointer-events: none;
  opacity: 0.06;
}

@media (max-width: 767px) {
  #particles-bg {
    display: none;
  }
}

/* ============================================================
   PHASE 5: ACCESSIBILITY
   ARIA roles applied via HTML attributes, not CSS.
   See index.html and component JS for role declarations.
   ============================================================ */