:root {
  /* Core neutrals */
  --bg: #F5F7FA;
  --card: #FFFFFF;
  --border: #E8ECF0;
  --muted: #6B7280;
  --text: #1F2937;

  /* Muted blue-gray accents */
  --accent-blue: #6B8FA3;
  --accent-blue-light: #8FA8B8;
  --accent-blue-lighter: #A8BCC8;
  --accent-blue-bg: #E8F0F5;
  --accent-blue-border: #B8D0E0;
  
  /* Secondary purple accents */
  --accent-purple: #8B7FA8;
  --accent-purple-light: #A89BC4;
  --accent-purple-bg: #F0EDF5;
  --accent-purple-border: #D4C8E0;
  
  /* Tertiary warm coral accents */
  --accent-coral: #C98A7A;
  --accent-coral-light: #D9A99A;
  --accent-coral-bg: #F5EDEA;
  --accent-coral-border: #E8D4C8;
  
  /* Accent indigo */
  --accent-indigo: #6B7FA8;
  --accent-indigo-light: #8B9BC4;
  --accent-indigo-bg: #EDF0F5;
  --accent-indigo-border: #C8D0E0;

  --pill: #F0F4F8;
  --pill-border: #D1D9E0;

  /* Status colors with blue-gray influence */
  --good-bg: #E8F5E9;
  --good-border: #A5D6A7;
  --good-text: #2E7D32;

  --warn-bg: #FFF3E0;
  --warn-border: #FFCC80;
  --warn-text: #E65100;

  --bad-text: #C62828;
  --bad-bg: #FFEBEE;
  --bad-border: #EF9A9A;

  /* Figure (coordinate plots, diagrams) – light mode */
  --figure-grid: rgba(0, 0, 0, 0.06);
  --figure-axis: #374151;
  --figure-label: #1f2937;
  --figure-line: #5b7fa3;
  --figure-point-fill: #c9a26a;
  --figure-point-stroke: #374151;
}

/* Dark mode */
[data-theme="dark"] {
  /* Core neutrals */
  --bg: #1A1D24;
  --card: #252932;
  --border: #2D3440;
  --muted: #8B92A8;
  --text: #E4E7EB;

  /* Muted blue-gray accents - adjusted for dark */
  --accent-blue: #7BA3C0;
  --accent-blue-light: #8FB5D0;
  --accent-blue-lighter: #A8C5DB;
  --accent-blue-bg: #2A3440;
  --accent-blue-border: #3D4A5A;
  
  /* Secondary purple accents */
  --accent-purple: #9B8FB8;
  --accent-purple-light: #B5A8D0;
  --accent-purple-bg: #2D2838;
  --accent-purple-border: #3D3548;
  
  /* Tertiary warm coral accents */
  --accent-coral: #D99A8A;
  --accent-coral-light: #E9B5AA;
  --accent-coral-bg: #3A2E2A;
  --accent-coral-border: #4A3D38;
  
  /* Accent indigo */
  --accent-indigo: #7B8FB8;
  --accent-indigo-light: #9BA8D0;
  --accent-indigo-bg: #2A2D38;
  --accent-indigo-border: #3D4048;

  --pill: #2D3440;
  --pill-border: #3D4550;

  /* Status colors - adjusted for dark */
  --good-bg: #1E3A2E;
  --good-border: #2D5A3D;
  --good-text: #81C995;

  --warn-bg: #3A2E1E;
  --warn-border: #5A4530;
  --warn-text: #FFB366;

  --bad-text: #FF6B6B;
  --bad-bg: #3A2525;
  --bad-border: #5A3535;

  /* Figure – dark mode */
  --figure-grid: rgba(255, 255, 255, 0.08);
  --figure-axis: #e5e7eb;
  --figure-label: #e4e7eb;
  --figure-line: #7ba8d0;
  --figure-point-fill: #d4a574;
  --figure-point-stroke: #e5e7eb;
}

* { box-sizing: border-box; }
html, body {
  height: 100%;
  margin: 0;
}
body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen', 'Ubuntu', 'Cantarell', 'Fira Sans', 'Droid Sans', 'Helvetica Neue', sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

#app {
  display: flex;
  flex-direction: column;
  min-height: 100%;
  height: 100vh;
  overflow: hidden;
}

a { color: inherit; text-decoration: none; }
a:hover { text-decoration: underline; }

.topbar {
  flex-shrink: 0;
  position: sticky;
  top: 0;
  z-index: 50;
  background: var(--card);
  border-bottom: 1px solid var(--accent-blue-border);
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
  backdrop-filter: blur(10px);
}
[data-theme="dark"] .topbar {
  background: rgba(37, 41, 50, 0.95);
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.3);
}
.topbar-inner {
  width: 100%;
  max-width: 1400px;
  margin: 0 auto;
  padding: 16px 24px;
  display: flex;
  align-items: center;
  gap: 20px;
}

@media (min-width: 900px) {
  .topbar-inner {
    max-width: 100%;
    padding-left: 48px;
    padding-right: 48px;
  }
}

.brand {
  font-size: 24px;
  font-weight: 700;
  text-decoration: none;
  color: inherit;
  cursor: pointer;
}
.brand:hover {
  opacity: 0.85;
  text-decoration: none;
}
.nav {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-left: auto;
}
.nav .nav-stats-profile-wrap {
  display: contents;
}
.nav a {
  border: 1px solid var(--accent-blue-border);
  background: var(--card);
  border-radius: 7px;
  padding: 7px 16px;
  font-size: 13.5px;
  font-weight: 500;
  color: var(--text);
  transition: all 0.2s ease;
}
.nav a:hover {
  background: var(--accent-blue-bg);
  border-color: var(--accent-blue-light);
  text-decoration: none;
}
.nav a.active {
  background: var(--accent-blue-light);
  border-color: var(--accent-blue-light);
  color: #fff;
  font-weight: 600;
}
.nav .nav-current {
  display: inline-block;
  border: 1px solid var(--accent-blue-light);
  background: var(--accent-blue-light);
  border-radius: 7px;
  padding: 7px 16px;
  font-size: 13.5px;
  color: #fff;
  font-weight: 600;
  cursor: default;
  pointer-events: none;
  text-decoration: none;
}
.nav-link.nav-link-locked {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  border: 1px solid var(--border);
  background: var(--pill);
  border-radius: 7px;
  padding: 7px 16px;
  font-size: 13.5px;
  color: var(--muted);
  cursor: default;
  opacity: 0.85;
  text-decoration: none;
  pointer-events: none;
}
.nav-link.nav-link-locked:hover {
  background: var(--pill);
  border-color: var(--border);
  color: var(--muted);
}
.nav .nav-lock-icon {
  width: 14px;
  height: 14px;
  flex-shrink: 0;
  color: var(--muted);
}

.nav-auth {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  transition: opacity 0.2s ease;
}
body.clerk-ready .nav-auth {
  opacity: 1;
}

.nav-home {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 7px 12px;
}
.nav-home .nav-home-icon {
  display: block;
}

/* Dark mode toggle button */
.dark-mode-toggle {
  background: var(--card);
  border: 1px solid var(--accent-blue-border);
  border-radius: 7px;
  padding: 7px 16px;
  cursor: pointer;
  font-size: 13.5px;
  font-weight: 500;
  line-height: 1;
  transition: all 0.2s ease;
  color: var(--text);
  margin-left: 8px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  white-space: nowrap;
}
.dark-mode-toggle:hover {
  background: var(--accent-blue-bg);
  border-color: var(--accent-blue-light);
  transform: scale(1.05);
}

.app {
  display: flex;
  flex: 1;
  min-height: 0;
  overflow: hidden;
  align-items: stretch;
}

/* Sidebar – fills space below topbar, own scrollbar */
.sidebar {
  width: 380px;
  flex-shrink: 0;
  background: var(--card);
  border-right: 1px solid var(--accent-blue-border);
  padding: 16px 20px;
  overflow-y: auto;
  overflow-x: hidden;
  overscroll-behavior: contain;
  box-sizing: border-box;
  scrollbar-width: thin;
  scrollbar-color: var(--accent-blue-light) var(--accent-blue-bg);
}
.sidebar::-webkit-scrollbar {
  width: 10px;
}
.sidebar::-webkit-scrollbar-track {
  background: var(--accent-blue-bg);
  border-radius: 5px;
}
.sidebar::-webkit-scrollbar-thumb {
  background: var(--accent-blue-light);
  border-radius: 5px;
}
.sidebar::-webkit-scrollbar-thumb:hover {
  background: var(--accent-blue);
}

.sidebar-note { 
  font-size: 12.5px; 
  color: var(--muted); 
  width: 100%;
  line-height: 1.6;
  flex: 0 0 auto;
  background: var(--pill);
  border: 1px solid var(--pill-border);
  border-radius: 8px;
  padding: 12px 16px;
  transition: all 0.2s ease;
}
.sidebar-note:hover {
  background: var(--border);
  border-color: var(--muted);
  transform: translateY(-1px);
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}
.sidebar-note:not(.collapsed):hover {
  transform: none;
  box-shadow: none;
}
.sidebar-note:not(.collapsed) {
  background: var(--pill);
  border-color: var(--pill-border);
}
.sidebar-note-header {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  user-select: none;
  margin-bottom: 8px;
}
.sidebar-note.collapsed .sidebar-note-header {
  margin-bottom: 0;
}
.sidebar-note-header:hover {
  opacity: 0.9;
}
.sidebar-note-chevron {
  position: absolute;
  left: 0;
  font-size: 14px;
  font-weight: 600;
  color: var(--muted);
  width: 18px;
  height: 18px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 4px;
  background: var(--border);
  transition: all 0.2s ease;
}
.sidebar-note-header:hover .sidebar-note-chevron {
  background: var(--muted);
  color: var(--card);
}
.sidebar-note-title {
  text-align: center;
  font-weight: 600;
  color: var(--text);
  margin: 0;
  font-size: 14px;
  width: 100%;
}
.sidebar-note-content {
  overflow: hidden;
  transition: max-height 0.3s ease, opacity 0.2s ease;
  max-height: 500px;
  opacity: 1;
}
.sidebar-note.collapsed .sidebar-note-content {
  max-height: 0;
  opacity: 0;
  margin: 0;
  padding: 0;
}
.sidebar-note-p {
  margin: 0 0 6px 0;
}
.sidebar-note-p:last-child {
  margin-bottom: 0;
}
.legend-box {
  display: inline-block;
  width: 12px;
  height: 12px;
  border-radius: 3px;
  border: 2px solid;
  margin: 0 4px 0 2px;
  vertical-align: middle;
  position: relative;
  overflow: hidden;
}
.legend-box-tan {
  background: var(--warn-bg);
  border-color: var(--warn-border);
}
.legend-box-green {
  background: var(--good-bg);
  border-color: var(--good-border);
}
.legend-box-gray {
  background: var(--border);
  border-color: var(--muted);
  opacity: 0.6;
}
.legend-box-gray::before,
.legend-box-gray::after {
  content: "";
  position: absolute;
  top: 50%;
  left: 50%;
  width: 1px;
  height: 16px;
  background: var(--muted);
  opacity: 0.9;
  transform-origin: center center;
}
.legend-box-gray::before {
  transform: translate(-50%, -50%) rotate(45deg);
}
.legend-box-gray::after {
  transform: translate(-50%, -50%) rotate(-45deg);
}
.legend-icon {
  display: inline-block;
  margin: 0 3px;
  vertical-align: middle;
  font-size: 14px;
}
.sidebar-top-actions {
  display: flex;
  flex-direction: column;
  gap: 12px;
  margin-bottom: 12px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--accent-blue-border);
}

.sidebar-expand-collapse-row {
  display: flex;
  flex-direction: row;
  gap: 8px;
  margin-bottom: 10px;
  align-items: stretch;
}
.sidebar-expand-collapse-btn {
  flex: 1;
  padding: 6px 10px;
  font-size: 12px;
  font-weight: 600;
  border: 1px solid var(--accent-blue-border);
  border-radius: 8px;
  background: var(--card);
  color: var(--text);
  cursor: pointer;
  transition: background 0.2s ease, border-color 0.2s ease;
}
.sidebar-expand-collapse-btn:hover {
  background: var(--accent-blue-bg);
  border-color: var(--accent-blue-light);
}

.topic {
  border: 1px solid var(--accent-blue-border);
  border-radius: 10px;
  margin-bottom: 10px;
  overflow: hidden;
  background: var(--card);
  transition: all 0.2s ease;
}
.topic:hover {
  border-color: var(--accent-blue-light);
  box-shadow: 0 2px 8px rgba(107, 143, 163, 0.1);
}
.topic-header {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 16px 18px;
  background: var(--card);
  border-bottom: 1px solid var(--accent-blue-border);
  cursor: pointer;
  user-select: none;
  transition: all 0.2s ease;
}
.topic-header:hover,
.topic-header.active {
  background: linear-gradient(to right, var(--accent-purple-bg) 0%, var(--accent-blue-bg) 100%);
}
.topic-chevron {
  font-size: 16px;
  font-weight: 600;
  color: var(--accent-indigo);
  width: 22px;
  height: 22px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 5px;
  background: var(--accent-indigo-bg);
  transition: all 0.2s ease;
  flex-shrink: 0;
}
.topic-header:hover .topic-chevron {
  background: var(--accent-indigo);
  color: #fff;
}
.topic-title { 
  font-weight: 600; 
  font-size: 14.5px; 
  color: var(--text);
  letter-spacing: 0.1px;
}
.topic-spacer { flex: 1; }

.icon-btn {
  border: 2px solid var(--text);
  background: var(--card);
  border-radius: 6px;
  padding: 6px 10px;
  cursor: pointer;
  font-size: 14px;
  line-height: 1;
  transition: all 0.2s ease;
  color: var(--text);
  font-weight: 600;
}
.topic-header .icon-btn {
  padding: 7px 11px;
  font-size: 15px;
}
.icon-btn:hover { 
  background: var(--accent-coral-bg); 
  border-color: var(--text);
}
#randomizeProblemBtn {
  border-color: var(--accent-blue-lighter);
  color: var(--accent-blue);
}
#randomizeProblemBtn:hover {
  background: var(--accent-blue-bg);
  border-color: var(--accent-blue);
}

.topic-body { 
  padding: 6px 18px 14px 18px; 
  display: none; 
  background: var(--card);
}
.topic-body.open { display: block; }

.q-row {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 10px 12px;
  border-radius: 7px;
  cursor: pointer;
  margin-bottom: 3px;
  transition: all 0.15s ease;
  border: 1px solid transparent;
}
.q-row:hover,
.q-row.active { 
  background: linear-gradient(to right, var(--accent-purple-bg) 0%, var(--accent-blue-bg) 100%); 
  border-color: transparent;
}
.q-row-locked {
  opacity: 0.7;
  cursor: default;
  background: var(--pill);
  border-color: var(--border);
}
.q-row-locked:hover {
  background: var(--pill);
  border-color: var(--border);
}
.q-row-lock-wrap {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-left: auto;
}
.q-row-lock-icon {
  width: 18px;
  height: 18px;
  color: var(--muted);
  flex-shrink: 0;
}
.q-row-lock-text {
  font-size: 11px;
  color: var(--muted);
  white-space: nowrap;
}

/* Locked page (Stats / Profile in demo mode) */
.page-locked {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 280px;
  padding: 24px;
}
.page-locked-wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
  padding: 32px;
  background: var(--pill);
  border: 1px solid var(--border);
  border-radius: 12px;
  text-align: center;
}
.page-locked-icon {
  width: 48px;
  height: 48px;
  color: var(--muted);
}
.page-locked-text {
  margin: 0;
  font-size: 1rem;
  color: var(--muted);
}
.page-locked-link {
  display: inline-block;
  padding: 10px 20px;
  font-size: 14px;
  font-weight: 600;
  color: #fff;
  background: linear-gradient(to right, var(--accent-purple) 0%, var(--accent-blue) 100%);
  border-radius: 7px;
  text-decoration: none;
}
.page-locked-link:hover {
  opacity: 0.95;
  text-decoration: none;
  color: #fff;
}

.q-title {
  font-size: 13px;
  color: var(--text);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  max-width: 180px;
  font-weight: 500;
}
.q-title.completed { color: var(--good-text); font-weight: 700; }
.q-title.wrong { color: var(--bad-text); font-weight: 700; }

.hint-boxes { display: flex; gap: 4px; margin-left: auto; }
.hint-box {
  width: 14px;
  height: 14px;
  border-radius: 3px;
  border: 2px solid var(--border);
  background: var(--card);
  transition: all 0.2s ease;
}
.hint-box.tan { 
  background: var(--warn-bg); 
  border-color: var(--warn-border); 
  border-width: 2px;
}
.hint-box.green { 
  background: var(--good-bg); 
  border-color: var(--good-border); 
  border-width: 2px;
}
.hint-box.gray {
  background: var(--border);
  border-color: var(--muted);
  border-width: 2px;
  opacity: 0.6;
  position: relative;
  overflow: hidden;
}
.hint-box.gray::before,
.hint-box.gray::after {
  content: "";
  position: absolute;
  top: 50%;
  left: 50%;
  width: 1px;
  height: 20px;
  background: var(--muted);
  opacity: 0.9;
  transform-origin: center center;
}
.hint-box.gray::before {
  transform: translate(-50%, -50%) rotate(45deg);
}
.hint-box.gray::after {
  transform: translate(-50%, -50%) rotate(-45deg);
}

.q-actions { display: flex; gap: 6px; margin-left: 6px; }

/* Main */
.main {
  flex: 1;
  min-height: 0;
  overflow-y: auto;
  padding: 40px 48px;
  background: var(--bg);
}
/* Hide raw LaTeX until MathJax has typeset */
.math-pending {
  visibility: hidden;
}

.container { max-width: 900px; margin: 0 auto; }
.loading-msg { color: var(--muted); font-size: 1rem; margin: 2rem 0; }

.demo-upgrade-banner {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 12px 16px;
  margin-bottom: 16px;
  font-size: 14px;
}
.demo-upgrade-banner a { color: var(--accent); font-weight: 600; }
.demo-upgrade-banner a:hover { text-decoration: underline; }

.card {
  background: var(--card);
  border: 1px solid var(--accent-blue-border);
  border-radius: 14px;
  padding: 32px 36px;
  margin-bottom: 24px;
  box-shadow: 0 1px 3px rgba(201, 125, 96, 0.08);
  transition: all 0.2s ease;
}
.card:hover {
  box-shadow: 0 4px 12px rgba(107, 143, 163, 0.12);
  border-color: var(--accent-blue-light);
}
header h1 { 
  margin: 0 0 10px 0; 
  font-size: 34px; 
  color: var(--text);
  font-weight: 700;
  letter-spacing: -0.5px;
}
header p { margin: 0; color: var(--muted); font-size: 15.5px; line-height: 1.6; }

.meta { display: flex; gap: 10px; flex-wrap: wrap; margin-top: 18px; color: var(--muted); font-size: 13.5px; }
.pill { 
  background: var(--pill); 
  border: 1px solid var(--pill-border); 
  border-radius: 999px; 
  padding: 6px 13px; 
  font-weight: 500;
  font-size: 12.5px;
}
.pill.good { background: var(--good-bg); border-color: var(--good-border); color: var(--good-text); }
.pill.warn { background: var(--warn-bg); border-color: var(--warn-border); color: var(--warn-text); }
.pill.bad { background: var(--bad-bg); border-color: var(--bad-border); color: var(--bad-text); }

h2 { 
  margin: 0 0 16px 0; 
  font-size: 24px; 
  color: var(--text);
  font-weight: 600;
  letter-spacing: -0.3px;
}
.problem-text { 
  font-size: 16.5px; 
  margin-bottom: 20px; 
  line-height: 1.75;
  color: var(--text);
}

button {
  border: 1px solid var(--accent-blue-border);
  background: var(--card);
  padding: 10px 18px;
  border-radius: 8px;
  cursor: pointer;
  font-size: 14px;
  font-weight: 500;
  color: var(--text);
  transition: all 0.2s ease;
}
button:hover { 
  background: var(--accent-purple-bg); 
  border-color: var(--accent-purple-light);
  transform: translateY(-1px);
  box-shadow: 0 2px 6px rgba(184, 93, 74, 0.15);
}
button:disabled { 
  cursor: not-allowed; 
  opacity: 0.5; 
  transform: none;
}
button.action-wide {
  background: var(--pill);
  border-color: var(--pill-border);
  color: var(--text);
  width: 100%;
  font-weight: 600;
  padding: 12px 16px;
}
button.action-wide:hover {
  background: var(--border);
  border-color: var(--muted);
  transform: translateY(-1px);
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.btn-row { display: flex; flex-wrap: wrap; gap: 12px; margin: 16px 0; }

/* Video solution box - under hints, collapsible */
.video-solution-box {
  margin-top: 16px;
  overflow: hidden;
  border-radius: 12px;
}
.video-solution-header {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px 16px;
  font-size: 14px;
  font-weight: 600;
  color: var(--text);
  background: var(--card);
  border: 1px solid var(--accent-blue-border);
  border-radius: 12px;
  cursor: default;
  user-select: none;
}
.video-solution-box.expandable .video-solution-header {
  cursor: pointer;
}
.video-solution-box.expandable .video-solution-header:hover {
  background: var(--accent-blue-bg);
  border-color: var(--accent-blue-light);
}
.video-solution-title {
  flex-shrink: 0;
}
.video-solution-locked {
  font-size: 12px;
  font-weight: 500;
  color: var(--muted);
}
.video-solution-box.expandable .video-solution-locked {
  display: none;
}
.video-solution-chevron {
  margin-left: auto;
  font-size: 14px;
  color: var(--muted);
  transition: transform 0.2s ease;
}
.video-solution-box:not(.expandable) .video-solution-chevron {
  display: none;
}
.video-solution-box.expandable.expanded .video-solution-chevron {
  transform: rotate(180deg);
}
.video-solution-body {
  display: none;
  padding: 12px 16px 16px;
  border: 1px solid var(--accent-blue-border);
  border-top: none;
  border-radius: 0 0 12px 12px;
  background: var(--card);
}
.video-solution-box.expanded .video-solution-body {
  display: block;
}
.video-solution-body iframe {
  display: block;
  width: 100%;
  max-width: 720px;
  margin: 0 auto;
  aspect-ratio: 16 / 9;
  border: none;
  border-radius: 8px;
  background: var(--border);
}

.hint, .solution { 
  border-left: 3px solid var(--accent-indigo); 
  padding: 18px 22px; 
  background: var(--accent-indigo-bg); 
  margin-top: 16px; 
  display: none; 
  border-radius: 0 10px 10px 0;
  box-shadow: 0 1px 2px rgba(168, 93, 74, 0.08);
  line-height: 1.7;
}
.solution { 
  border-left-color: var(--accent-purple); 
  background: linear-gradient(to right, var(--accent-purple-bg) 0%, var(--accent-indigo-bg) 100%);
}

.small { font-size: 13px; color: var(--muted); }

/* Code styling - clean, no boxes */
code {
  background: transparent;
  padding: 0;
  border-radius: 0;
  font-family: 'Courier New', Courier, monospace;
  font-size: 0.95em;
  color: var(--text);
  font-weight: 500;
  border: none;
}

/* MathJax equation styling - clean and readable */
.hint .MathJax,
.solution .MathJax,
.hint mjx-container,
.solution mjx-container,
.mc-option .MathJax,
.mc-option mjx-container,
.figure-figure-label .MathJax,
.figure-figure-label mjx-container {
  display: inline-block;
  margin: 0 2px;
  vertical-align: middle;
  font-weight: 400; /* Match regular text weight */
}

/* Style for inline math in hints/solutions */
.hint code, .solution code {
  background: transparent;
  padding: 0;
  border: none;
  font-family: 'Courier New', Courier, monospace;
  font-size: 0.95em;
  color: var(--text);
  display: inline;
  line-height: 1.6;
}

/* Make sure MathJax renders nicely with matching font weight */
mjx-container {
  display: inline-block;
  margin: 0 2px;
  font-weight: 400; /* Match regular text weight */
}

/* Target MathJax math elements to ensure consistent weight */
mjx-math {
  font-weight: 400 !important;
}

/* Target MathJax text elements */
mjx-mtext {
  font-weight: 400 !important;
}

/* Target all MathJax elements to match regular text weight */
mjx-container * {
  font-weight: 400 !important;
}

.top-actions { display: flex; gap: 12px; flex-wrap: wrap; margin-top: 16px; align-items: center; }
.row { display: flex; gap: 12px; flex-wrap: wrap; align-items: center; }

.problem-figure {
  margin-top: 12px;
  margin-bottom: 20px;
  text-align: center;
}
.problem-figure-img {
  max-width: 100%;
  height: auto;
  border-radius: 10px;
  border: 1px solid var(--accent-blue-border);
  box-shadow: 0 1px 3px rgba(0,0,0,0.08);
}
.problem-figure-inline {
  display: block;
  max-width: 100%;
  margin: 0 auto;
}
.figure-figure-inner {
  position: relative;
  max-width: 840px;
  margin: 0 auto;
}
.problem-figure-inline .line-figure {
  display: block;
  width: 100%;
  height: auto;
  border-radius: 10px;
  overflow: visible;
}
.figure-figure-overlay {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
}
.figure-figure-label {
  position: absolute;
  color: var(--figure-label);
  font-size: 14.5px;
  font-weight: 400;
  font-family: inherit;
  white-space: nowrap;
}
.figure-figure-label mjx-container,
.figure-figure-label .MathJax {
  font-size: 1em;
  font-weight: 400;
  color: inherit;
}
.problem-figure-caption {
  margin: 8px 0 0 0;
  font-size: 13px;
  color: var(--muted);
}
.answer-options-wrap {
  display: flex;
  flex-direction: column;
  gap: 4px;
  flex: 0 0 auto;
  max-width: 280px;
}
.mc-option {
  text-align: left;
  padding: 5px 9px;
  border: 1px solid var(--accent-blue-border);
  background: var(--card);
  border-radius: 4px;
  cursor: pointer;
  font-family: inherit;
  font-size: 0.95em;
  line-height: 1.7;
  color: var(--text);
  transition: all 0.2s ease;
}
.mc-option mjx-container,
.mc-option .MathJax {
  font-size: 0.95em;
}
.mc-option:hover {
  background: var(--accent-blue-bg);
  border-color: var(--accent-blue-light);
}
.mc-option.selected {
  background: var(--accent-blue-bg);
  border-color: var(--accent-blue);
  font-weight: 500;
}

input[type="text"], input[type="date"], input[type="email"], textarea, select {
  padding: 11px 16px;
  border: 1px solid var(--accent-blue-border);
  border-radius: 8px;
  font-size: 14.5px;
  background: var(--card);
  color: var(--text);
  transition: all 0.2s ease;
  font-family: inherit;
}
input[type="text"]:focus, input[type="date"]:focus, input[type="email"]:focus, textarea:focus, select:focus {
  outline: none;
  border-color: var(--accent-coral);
  box-shadow: 0 0 0 3px rgba(201, 138, 122, 0.1);
}
[data-theme="dark"] input[type="text"]:focus,
[data-theme="dark"] input[type="date"]:focus,
[data-theme="dark"] input[type="email"]:focus,
[data-theme="dark"] textarea:focus,
[data-theme="dark"] select:focus {
  box-shadow: 0 0 0 3px rgba(217, 169, 154, 0.2);
}

/* Answer card styling */
.answer-card {
  background: var(--card) !important;
  border-color: var(--accent-blue-border) !important;
  padding: 18px 24px !important;
  transition: padding 0.2s ease;
}
.answer-card.has-feedback {
  padding: 32px 36px !important;
}
textarea { width: 100%; min-height: 120px; }

.status-line { margin-top: 16px; display: flex; gap: 12px; flex-wrap: wrap; }
.feedback { 
  font-size: 15px; 
  padding: 0;
  border-radius: 10px;
  font-weight: 500;
  line-height: 1.6;
  margin-top: 0;
  max-height: 0;
  overflow: hidden;
  transition: margin-top 0.2s ease, max-height 0.2s ease;
}
.feedback.has-content {
  margin-top: 18px;
  padding: 14px 18px;
  max-height: 200px;
}
.feedback.good { 
  color: var(--good-text); 
  background: var(--good-bg);
  border: 1px solid var(--good-border);
}
.feedback.bad { 
  color: var(--bad-text); 
  background: var(--bad-bg); 
  border: 1px solid var(--bad-border);
}

@keyframes feedback-vibrate {
  0%, 100% { transform: translateX(0); }
  15% { transform: translateX(-5px); }
  30% { transform: translateX(5px); }
  45% { transform: translateX(-4px); }
  60% { transform: translateX(4px); }
  75% { transform: translateX(-2px); }
  90% { transform: translateX(2px); }
}
.feedback.feedback-vibrate {
  animation: feedback-vibrate 0.6s ease-in-out;
}

#checkBtn {
  position: relative;
  transition: opacity 0.2s ease, border-color 0.2s ease, background 0.2s ease;
}
#checkBtn::before {
  content: "";
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: linear-gradient(to right, var(--accent-purple-bg) 0%, var(--accent-blue-bg) 100%);
  z-index: -1;
  pointer-events: none;
  transform-origin: left;
  transform: scaleX(0);
  clip-path: inset(0 0 0 100%);
}
#checkBtn.check-btn-disabled {
  opacity: 0.5;
  cursor: not-allowed;
  pointer-events: none;
}

@keyframes check-btn-nudge {
  0% { transform: scale(1); }
  30% { transform: scale(1.08); }
  60% { transform: scale(0.98); }
  100% { transform: scale(1); }
}

@keyframes check-btn-nudge-gradient {
  0% {
    transform: scaleX(0);
    clip-path: inset(0 0 0 100%);
  }
  20% {
    transform: scaleX(1);
    clip-path: inset(0 0 0 0);
  }
  100% {
    transform: scaleX(1);
    clip-path: inset(0 0 0 100%);
  }
}

#checkBtn.check-btn-nudge {
  animation: check-btn-nudge 0.5s ease;
  border-color: transparent;
  background: transparent;
}
#checkBtn.check-btn-nudge::before {
  animation: check-btn-nudge-gradient 0.48s ease-out;
}

button.hint-used {
  background: var(--warn-bg);
  border-color: var(--warn-border);
  color: var(--warn-text);
}

/* Modal */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  backdrop-filter: blur(4px);
  display: none;
  align-items: center;
  justify-content: center;
  padding: 20px;
  z-index: 9999;
}
[data-theme="dark"] .modal-overlay {
  background: rgba(0, 0, 0, 0.7);
}
.modal-overlay.open { display: flex; }
.modal {
  width: 100%;
  max-width: 480px;
  background: var(--card);
  border: 1px solid var(--accent-blue-border);
  border-radius: 14px;
  padding: 28px;
  box-shadow: 0 12px 32px rgba(107, 143, 163, 0.2);
}
.modal h3 { 
  margin: 0 0 14px 0; 
  font-size: 22px; 
  color: var(--text);
  font-weight: 600;
  letter-spacing: -0.3px;
}
.modal p { margin: 0 0 24px 0; color: var(--muted); line-height: 1.7; font-size: 15px; }
.modal-actions { display: flex; gap: 10px; justify-content: flex-end; }
.modal-actions button {
  padding: 10px 20px;
  font-weight: 500;
}
.modal-actions .danger {
  background: var(--bad-text);
  border-color: var(--bad-text);
  color: #fff;
}
.modal-actions .danger:hover { 
  background: #B71C1C; 
  border-color: #B71C1C;
}

@media (max-width: 980px) {
  .app { flex-direction: column; }
  .sidebar { width: 100%; border-right: none; border-bottom: 1px solid var(--border); }
}