/* === Custom Properties === */
:root {
  --color-dark: #334155;
  --color-secondary: #475569;
  --color-accent: #F87171;
  --color-highlight: #ef4444;
  --color-correct: #10b981;
  --color-bg: #F8FAFC;
  --color-card-bg: #ffffff;
  --color-text: #1E293B;
  --color-text-light: #64748B;
  --color-border: #E2E8F0;
  --radius: 8px;
  --shadow: 0 2px 8px rgba(0, 0, 0, 0.06);
  --shadow-hover: 0 4px 16px rgba(0, 0, 0, 0.10);
  --transition: 0.2s ease;
}

/* === Dark Theme === */
[data-theme="dark"] {
  --color-dark: #1E293B;
  --color-secondary: #475569;
  --color-accent: #FB923C;
  --color-highlight: #f87171;
  --color-correct: #34d399;
  --color-bg: #0F172A;
  --color-card-bg: #1E293B;
  --color-text: #E2E8F0;
  --color-text-light: #94A3B8;
  --color-border: #334155;
  --shadow: 0 2px 8px rgba(0, 0, 0, 0.3);
  --shadow-hover: 0 4px 16px rgba(0, 0, 0, 0.4);
}

[data-theme="dark"] .filter-bar select,
[data-theme="dark"] .filter-bar input[type="text"],
[data-theme="dark"] .multi-select__toggle,
[data-theme="dark"] .multi-select__panel {
  background: var(--color-card-bg);
  color: var(--color-text);
}

[data-theme="dark"] .filter-bar--chips {
  background: var(--color-card-bg);
}

[data-theme="dark"] .chip:hover {
  background: var(--color-card-bg);
}

[data-theme="dark"] .chip--excluded {
  background: transparent;
  color: var(--color-highlight);
  border-color: var(--color-highlight);
}

[data-theme="dark"] .chip--excluded:hover {
  background: rgba(239, 68, 68, 0.15);
}

[data-theme="dark"] .subtopic-group__summary {
  background: var(--color-card-bg);
}

[data-theme="dark"] .subtopic-group__summary:hover {
  background: var(--color-border);
}

[data-theme="dark"] .multi-select__panel label:hover {
  background: var(--color-bg);
}

[data-theme="dark"] .badge--stage,
[data-theme="dark"] .badge--course {
  background: #1e293b;
  color: #94a3b8;
  border-color: #334155;
}

/* === Theme Toggle Button === */
.theme-toggle {
  background: none;
  border: none;
  font-size: 1.25rem;
  cursor: pointer;
  padding: 0.25rem 0.4rem;
  border-radius: var(--radius);
  transition: opacity var(--transition);
  line-height: 1;
  color: rgba(255, 255, 255, 0.8);
  display: flex;
  align-items: center;
}

.theme-toggle:hover {
  opacity: 0.8;
}

/* === Site Footer === */
.site-footer {
  text-align: center;
  padding: 2rem 1rem;
  border-top: 1px solid var(--color-border);
  color: var(--color-text-light);
  font-size: 0.85rem;
  margin-top: 1rem;
}

.site-footer a {
  color: var(--color-text-light);
  text-decoration: none;
  transition: color var(--transition);
}

.site-footer a:hover {
  color: var(--color-text);
}

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

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
  min-height: 100vh;
}

/* === Header === */
.site-header {
  background: color-mix(in srgb, var(--color-accent) 40%, #000);
  color: #fff;
  padding: 1rem 2rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  position: sticky;
  top: 0;
  z-index: 100;
}

.site-header__title {
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  color: inherit;
  text-decoration: none;
}

.site-header__logo {
  flex-shrink: 0;
}

.site-header__nav {
  display: flex;
  align-items: center;
  gap: 1.5rem;
}

.site-header__nav a {
  color: rgba(255, 255, 255, 0.8);
  text-decoration: none;
  font-size: 1rem;
  font-weight: 500;
  transition: color var(--transition);
}

.site-header__nav a:hover,
.site-header__nav a.active {
  color: #fff;
}

/* === Main Content === */
.main-content {
  max-width: 1100px;
  margin: 0 auto;
  padding: 2rem;
}

/* === Filter Bar === */
.filter-bar {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
  margin-bottom: 2rem;
  align-items: center;
}

.filter-bar select,
.filter-bar input[type="text"] {
  padding: 0.5rem 0.75rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  font-family: inherit;
  font-size: 0.875rem;
  background: #fff;
  color: var(--color-text);
  min-width: 160px;
  transition: border-color var(--transition);
}

.filter-bar select:focus,
.filter-bar input[type="text"]:focus {
  outline: none;
  border-color: var(--color-accent);
}

.filter-bar__search {
  flex: 1;
  min-width: 120px;
}

.filter-row--search {
  flex-wrap: nowrap;
}

.filter-hint {
  font-size: 0.78rem;
  color: var(--color-text-light);
  margin: 0;
}

/* === Buttons === */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.5rem 1rem;
  border: none;
  border-radius: var(--radius);
  font-family: inherit;
  font-size: 0.875rem;
  font-weight: 500;
  cursor: pointer;
  transition: background var(--transition), transform var(--transition);
}

.btn:hover {
  transform: translateY(-1px);
}

.btn:active {
  transform: translateY(0);
}

.btn--primary {
  background: var(--color-dark);
  color: #fff;
}

.btn--primary:hover {
  background: var(--color-secondary);
}

[data-theme="dark"] .btn--primary {
  background: var(--color-accent);
}

[data-theme="dark"] .btn--primary:hover {
  opacity: 0.85;
  background: var(--color-accent);
}

.btn--secondary {
  background: var(--color-card-bg);
  color: var(--color-text);
  border: 1px solid var(--color-border);
}

.btn--danger {
  background: var(--color-highlight);
  color: #fff;
}

.btn--correct {
  background: var(--color-correct);
  color: #fff;
}

.btn--success {
  background: #F87171;
  color: #fff;
}

.btn--success:hover {
  background: #ef4444;
}

.btn--print {
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  line-height: 1.2;
  gap: 0.2rem;
}

.btn--small {
  padding: 0.4rem 0.8rem;
  font-size: 0.8rem;
}

/* === Toast Notification === */
.toast {
  position: fixed;
  top: 2rem;
  left: 50%;
  transform: translateX(-50%) translateY(-1rem);
  padding: 0.75rem 1.25rem;
  border-radius: var(--radius);
  color: #fff;
  font-weight: 500;
  font-size: 0.9rem;
  z-index: 1000;
  opacity: 0;
  transition: opacity 0.3s, transform 0.3s;
  pointer-events: none;
}

.toast--visible {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
}

.toast--success {
  background: var(--color-correct);
}

.toast--error {
  background: var(--color-highlight);
}

/* === Badge / Pill === */
.badge {
  display: inline-block;
  padding: 0.15rem 0.5rem;
  border-radius: 100px;
  font-size: 0.7rem;
  font-weight: 600;
  letter-spacing: 0.03em;
}

.badge--stage,
.badge--course {
  background: #f1f5f9;
  color: #475569;
  border: 1px solid #cbd5e1;
}

.badge--topic {
  background: var(--color-secondary);
  color: #fff;
}

.badge--difficulty {
  background: var(--color-card-bg);
  color: var(--color-text);
  border: 1px solid var(--color-border);
}


/* === Loading === */
.loading {
  text-align: center;
  padding: 3rem;
  color: var(--color-text-light);
}

.empty-state {
  text-align: center;
  padding: 4rem 2rem;
  color: var(--color-text-light);
}

/* === Responsive === */
@media (max-width: 768px) {
  .site-header {
    flex-direction: column;
    gap: 0.5rem;
    padding: 0.75rem 1rem;
  }

  .main-content {
    padding: 1rem;
  }

  .filter-bar {
    flex-direction: column;
  }

  .filter-bar select,
  .filter-bar input[type="text"] {
    width: 100%;
  }

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

  .filter-col--right {
    border-left: none;
    padding-left: 0;
    border-top: 1px solid var(--color-border);
    padding-top: 0.75rem;
  }
}

@media (max-width: 480px) {
  .site-header__nav {
    gap: 1rem;
    font-size: 0.8rem;
  }
}

/* === KaTeX === */
.katex-display {
  text-align: left !important;
  margin: 0.5em 0 !important;
}
.katex-display > .katex {
  display: inline-block !important;
}

/* === Filter Row (chips mode) === */
.filter-bar--chips {
  flex-direction: column;
  align-items: stretch;
  gap: 0.75rem;
  background: #fff;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1rem 1.25rem;
  box-shadow: var(--shadow);
}

.filter-columns {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.5rem;
  align-items: start;
}

.filter-col {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.filter-col--right {
  border-left: 1px solid var(--color-border);
  padding-left: 1.5rem;
}

.filter-row {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 0.5rem;
  row-gap: 0.4rem;
}

.filter-row__label {
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--color-highlight);
  white-space: nowrap;
  letter-spacing: 0.06em;
}

.subtopic-group__summary .filter-row__label[class*="badge--topic"],
[data-theme="dark"] .subtopic-group__summary .filter-row__label[class*="badge--topic"] {
  background: none;
  border: none;
  padding: 0;
}

.filter-row--topic {
  padding-block: 0.3rem;
}

.filter-row--topic .filter-row__label {
  flex-basis: 100%;
}

.filter-row--topic .filter-row__label.badge {
  flex-basis: auto;
  flex-shrink: 0;
  margin-left: -0.5rem;
  margin-right: 100%;
}

.filter-row--action {
  display: flex;
  justify-content: flex-end;
}

.subtopic-heading {
  margin: 0;
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--color-highlight);
  letter-spacing: 0.06em;
}

#subtopic-filter {
  display: flex;
  flex-wrap: wrap;
  gap: 0.25rem;
}

.subtopic-group {
  display: inline-flex;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  overflow: hidden;
  vertical-align: top;
}

.subtopic-group[open] {
  display: flex;
  flex-basis: 100%;
}

.subtopic-group__summary {
  display: flex;
  align-items: center;
  padding: 0.25rem 0.5rem;
  cursor: pointer;
  user-select: none;
  background: var(--color-bg);
  list-style: none;
  gap: 0.35rem;
}

.subtopic-group__summary::-webkit-details-marker {
  display: none;
}

.subtopic-group__summary::before {
  content: '▸';
  font-size: 0.8rem;
  color: var(--color-text-light);
  transition: transform var(--transition);
  flex-shrink: 0;
}

.subtopic-group[open] > .subtopic-group__summary::before {
  transform: rotate(90deg);
}

.subtopic-group__summary .filter-row__label {
  min-width: 0;
  font-size: 0.82rem;
}

.subtopic-group__summary:hover {
  background: var(--color-border);
}

.subtopic-group__count {
  font-size: 0.7rem;
  font-weight: 600;
  padding: 0.05rem 0.4rem;
  border-radius: 100px;
  white-space: nowrap;
}

.subtopic-group__count:empty {
  display: none;
}

.subtopic-group__count--active {
  background: var(--color-highlight);
  color: #fff;
}

.subtopic-group__count--excluded {
  background: transparent;
  color: var(--color-highlight);
  border: 1px solid var(--color-highlight);
}

.subtopic-group > .filter-row--subtopic {
  padding: 0.3rem 0.5rem;
  border-top: 1px solid var(--color-border);
}

.chip {
  display: inline-flex;
  align-items: center;
  padding: 0.35rem 0.85rem;
  border-radius: 100px;
  font-size: 0.85rem;
  font-weight: 500;
  border: 1.5px solid var(--color-border);
  background: var(--color-bg);
  color: var(--color-text);
  cursor: pointer;
  transition: background var(--transition), color var(--transition), border-color var(--transition), box-shadow var(--transition);
  user-select: none;
  line-height: 1.3;
}

.chip:hover {
  border-color: var(--color-accent);
  color: var(--color-accent);
  background: #fff;
  box-shadow: 0 1px 4px rgba(59, 130, 246, 0.2);
}

.chip--active {
  background: var(--color-highlight);
  color: #fff;
  border-color: var(--color-highlight);
  box-shadow: 0 2px 6px rgba(59, 130, 246, 0.35);
}

.chip--active:hover {
  background: var(--color-accent);
  border-color: var(--color-accent);
  color: #fff;
}

.chip--excluded {
  background: transparent;
  color: var(--color-highlight);
  border-color: var(--color-highlight);
  text-decoration: line-through;
  opacity: 0.75;
}

.chip--excluded:hover {
  opacity: 1;
  background: rgba(239, 68, 68, 0.08);
  border-color: var(--color-highlight);
  color: var(--color-highlight);
}

.chip--dimmed {
  opacity: 0.38;
}

.chip--dimmed:hover {
  opacity: 1;
  border-color: var(--color-accent);
  color: var(--color-accent);
}

.chip input[type="checkbox"] {
  display: none;
}

.filter-bar--pending {
  border-color: var(--color-accent);
  box-shadow: 0 0 0 1px var(--color-accent);
  transition: border-color 0.2s, box-shadow 0.2s;
}

.filter-row--subtopic {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 0.5rem;
  row-gap: 0.4rem;
}

.filter-row__empty {
  font-size: 0.85rem;
  color: var(--color-muted);
  font-style: italic;
}

/* === Course prompt state === */
body.course-prompt .worksheet-controls,
body.course-prompt .worksheet-layout {
  opacity: 0.25;
  pointer-events: none;
  transition: opacity 0.3s;
}

body.course-prompt .filter-bar--chips {
  box-shadow: 0 0 0 3px var(--color-highlight), var(--shadow);
  position: relative;
  z-index: 1;
  transition: box-shadow 0.3s;
}

body.course-prompt #course-filter .chip {
  position: relative;
  overflow: hidden;
}

body.course-prompt #course-filter .chip::after {
  content: '';
  position: absolute;
  inset: 0;
  background: linear-gradient(90deg, transparent 0%, color-mix(in srgb, var(--color-accent) 35%, transparent) 50%, transparent 100%);
  background-size: 200% 100%;
  animation: course-shimmer 2.2s linear infinite;
  pointer-events: none;
}

@keyframes course-shimmer {
  0%   { background-position: -200% 0; }
  100% { background-position:  200% 0; }
}

/* === Multi-Select Dropdown === */
.multi-select {
  position: relative;
  display: inline-block;
}

.multi-select__toggle {
  padding: 0.5rem 2rem 0.5rem 0.75rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  font-family: inherit;
  font-size: 0.875rem;
  background: #fff;
  color: var(--color-text);
  min-width: 160px;
  cursor: pointer;
  text-align: left;
  transition: border-color var(--transition);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  position: relative;
}

.multi-select__toggle::after {
  content: " \25be";
  position: absolute;
  right: 0.6rem;
  top: 50%;
  transform: translateY(-50%);
  pointer-events: none;
}

.filters--loading {
  pointer-events: none;
  opacity: 0.5;
  cursor: not-allowed;
}

/* === Expand dropdown === */
.expand-dropdown {
  position: relative;
  display: inline-block;
}

.expand-dropdown > summary {
  list-style: none;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
}

.expand-dropdown > summary::-webkit-details-marker { display: none; }

.expand-dropdown__menu {
  position: absolute;
  top: calc(100% + 4px);
  right: 0;
  z-index: 100;
  background: var(--color-card-bg);
  border: 1px solid var(--color-border);
  border-radius: 6px;
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  min-width: 120px;
  overflow: hidden;
}

.expand-dropdown__item {
  padding: 0.45rem 0.9rem;
  text-align: left;
  background: none;
  border: none;
  cursor: pointer;
  font-size: 0.8rem;
  color: var(--color-text);
  white-space: nowrap;
}

.expand-dropdown__item:hover {
  background: var(--color-bg);
}

.multi-select__toggle:focus {
  outline: none;
  border-color: var(--color-accent);
}

.multi-select__panel {
  display: none;
  position: absolute;
  top: calc(100% + 4px);
  left: 0;
  min-width: 100%;
  background: #fff;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  box-shadow: var(--shadow-hover);
  z-index: 200;
  max-height: 220px;
  overflow-y: auto;
  padding: 0.25rem 0;
}

.multi-select.open .multi-select__panel {
  display: block;
}

.multi-select__panel label {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.4rem 0.75rem;
  cursor: pointer;
  font-size: 0.875rem;
  transition: background var(--transition);
}

.multi-select__panel label:hover {
  background: var(--color-card-bg);
}

.multi-select__panel input[type="checkbox"] {
  cursor: pointer;
  accent-color: var(--color-accent);
}

@media (max-width: 768px) {
  .multi-select__toggle {
    width: 100%;
  }
  .multi-select {
    width: 100%;
  }
}

/* === Auth Login Gate === */
.auth-login {
  text-align: center;
  padding: 4rem 2rem;
  max-width: 400px;
  margin: 0 auto;
}
.auth-login__title {
  font-size: 1.4rem;
  font-weight: 700;
  color: var(--color-text);
  margin: 0 0 1.5rem;
}
.auth-login__error {
  color: var(--color-highlight);
  font-size: 0.85rem;
  margin: 0 0 1rem;
}
.auth-login__hint {
  font-size: 0.82rem;
  color: var(--color-text-light);
  margin: 0.5rem 0 0;
}
.auth-login__divider {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin: 1.5rem 0;
  color: var(--color-text-light);
  font-size: 0.82rem;
}
.auth-login__divider::before,
.auth-login__divider::after {
  content: '';
  flex: 1;
  height: 1px;
  background: var(--color-border);
}
.auth-login__form {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}
.auth-login__form input {
  padding: 0.65rem 0.85rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  font-size: 0.9rem;
  background: var(--color-card-bg);
  color: var(--color-text);
}
.auth-login__form input:focus {
  outline: none;
  border-color: var(--color-accent);
}

/* Google Sign-In Button */
.btn--google {
  display: inline-flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.7rem 1.5rem;
  background: #fff;
  color: #3c4043;
  border: 1px solid #dadce0;
  border-radius: var(--radius);
  font-size: 0.95rem;
  font-weight: 500;
  cursor: pointer;
  transition: box-shadow var(--transition), background var(--transition);
}
.btn--google:hover {
  box-shadow: 0 1px 3px rgba(0,0,0,0.12);
  background: #f8f9fa;
}
[data-theme="dark"] .btn--google {
  background: #4285f4;
  color: #fff;
  border-color: #4285f4;
}
[data-theme="dark"] .btn--google:hover {
  background: #3367d6;
}

/* === Auth Header Widget === */
.auth-widget {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}
.auth-widget__avatar {
  width: 32px;
  height: 32px;
  border-radius: 50%;
  border: 2px solid rgba(255,255,255,0.3);
  object-fit: cover;
}
.auth-widget__avatar--initials {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  background: var(--color-accent);
  color: #fff;
  font-weight: 600;
  font-size: 0.85rem;
}
.auth-widget__name {
  font-size: 0.82rem;
  color: rgba(255,255,255,0.8);
  max-width: 120px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.auth-widget__signout {
  background: none;
  border: 1px solid rgba(255,255,255,0.3);
  color: rgba(255,255,255,0.8);
  padding: 0.25rem 0.6rem;
  border-radius: var(--radius);
  font-size: 0.78rem;
  cursor: pointer;
  transition: color var(--transition), border-color var(--transition);
}
.auth-widget__signout:hover {
  color: #fff;
  border-color: rgba(255,255,255,0.6);
}

@media (max-width: 768px) {
  .auth-widget__name {
    display: none;
  }
}

/* === Difficulty Info Button === */
.info-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  border: 1.5px solid currentColor;
  background: transparent;
  font-size: 0.75rem;
  font-weight: 700;
  font-style: normal;
  cursor: pointer;
  color: var(--color-muted);
  margin-left: 4px;
  padding: 0;
  line-height: 1;
  vertical-align: middle;
}
.info-btn:hover {
  color: var(--color-primary);
  border-color: var(--color-primary);
}

/* === Difficulty Info Popover === */
.difficulty-info-popover {
  position: absolute;
  z-index: 310;
  width: 480px;
  max-width: calc(100vw - 2rem);
  background: var(--color-card-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  box-shadow: var(--shadow-hover);
  padding: 1rem;
  font-size: 0.85rem;
}
.difficulty-info-popover__header {
  font-weight: 600;
  font-size: 0.95rem;
  margin-bottom: 0.6rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
}
.difficulty-info-popover__close {
  background: none;
  border: none;
  font-size: 1.2rem;
  line-height: 1;
  cursor: pointer;
  color: var(--color-muted);
  padding: 0 0 0 0.5rem;
}
.difficulty-info-popover__close:hover {
  color: var(--color-text);
}
.difficulty-info-popover__body p {
  margin: 0 0 0.5rem;
  line-height: 1.5;
}
.difficulty-info-popover__table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 0.25rem;
  font-size: 0.82rem;
}
.difficulty-info-popover__table th,
.difficulty-info-popover__table td {
  text-align: left;
  padding: 0.3rem 0.5rem;
  border: 1px solid var(--color-border);
}
.difficulty-info-popover__table th {
  font-weight: 600;
  background: var(--color-bg);
}