:root {
  --bg-main: #f8fafc;
  --bg-surface: #ffffff;
  --bg-card: rgba(255, 255, 255, 0.95);
  --border-color: rgba(226, 232, 240, 0.85);
  --text-main: #0f172a;
  --text-muted: #64748b;
  --primary: #0284c7;
  --primary-hover: #0369a1;
  --primary-light: #f0f9ff;
  --secondary: #059669;
  --secondary-light: #ecfdf5;
  --success: #10b981;
  --success-light: #ecfdf5;
  --warning: #f59e0b;
  --warning-light: #fffbeb;
  --danger: #ef4444;
  --danger-light: #fef2f2;
  --purple: #8b5cf6;
  --purple-light: #f5f3ff;
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.06);
  --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.08), 0 2px 4px -2px rgba(0,0,0,0.05);
  --shadow-lg: 0 12px 28px -6px rgba(2, 132, 199, 0.15);
  --transition: all 0.22s ease;
}

[data-theme="dark"] {
  --bg-main: #04121d;
  --bg-surface: #0a1e2e;
  --bg-card: rgba(10, 30, 46, 0.92);
  --border-color: rgba(30, 68, 99, 0.7);
  --text-main: #f8fafc;
  --text-muted: #94a3b8;
  --primary: #38bdf8;
  --primary-hover: #7dd3fc;
  --primary-light: rgba(56, 189, 248, 0.15);
  --secondary: #34d399;
  --secondary-light: rgba(52, 211, 153, 0.15);
  --success-light: rgba(16, 185, 129, 0.15);
  --warning-light: rgba(245, 158, 11, 0.15);
  --danger-light: rgba(239, 68, 68, 0.15);
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.3);
  --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.4);
  --shadow-lg: 0 12px 28px -6px rgba(0,0,0,0.6);
}

* { margin:0; padding:0; box-sizing:border-box; }
body {
  font-family: 'Plus Jakarta Sans', sans-serif;
  background: var(--bg-main);
  color: var(--text-main);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  transition: background 0.3s ease, color 0.3s ease;
}

/* NAVBAR */
.navbar {
  position: sticky;
  top: 0;
  z-index: 50;
  background: var(--bg-card);
  backdrop-filter: blur(14px);
  border-bottom: 1px solid var(--border-color);
  padding: 0.75rem 1.5rem;
}
.navbar-container {
  max-width: 1200px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}
.nav-left {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}
.btn-back {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  color: var(--text-main);
  text-decoration: none;
  font-size: 0.84rem;
  font-weight: 700;
  padding: 0.4rem 0.85rem;
  border-radius: 999px;
  transition: var(--transition);
}
.btn-back:hover {
  border-color: var(--primary);
  color: var(--primary);
}
.nav-title {
  font-family: 'Outfit', sans-serif;
  font-weight: 700;
  font-size: 1.05rem;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}
.nav-badge {
  font-size: 0.75rem;
  font-weight: 700;
  padding: 0.15rem 0.55rem;
  border-radius: 999px;
  background: var(--primary-light);
  color: var(--primary);
}
.nav-right {
  display: flex;
  align-items: center;
  gap: 0.85rem;
}
.theme-btn {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  color: var(--text-main);
  width: 36px;
  height: 36px;
  border-radius: 50%;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: var(--transition);
}
.theme-btn:hover {
  border-color: var(--primary);
  transform: scale(1.05);
}

/* HERO HEADER */
.hero {
  background: linear-gradient(135deg, rgba(2, 132, 199, 0.09) 0%, rgba(5, 150, 105, 0.08) 100%);
  border-bottom: 1px solid var(--border-color);
  padding: 2.5rem 1.5rem 2rem;
  text-align: center;
}
.hero-container {
  max-width: 900px;
  margin: 0 auto;
}
.hero-pill {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: 0.25rem 0.85rem;
  border-radius: 999px;
  background: var(--primary-light);
  color: var(--primary);
  margin-bottom: 1rem;
}
.hero-title {
  font-family: 'Outfit', sans-serif;
  font-size: 2.2rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  margin-bottom: 0.75rem;
  color: var(--text-main);
}
.hero-subtitle {
  color: var(--text-muted);
  font-size: 1.05rem;
  max-width: 680px;
  margin: 0 auto 1.5rem;
}
.progress-summary {
  display: inline-flex;
  align-items: center;
  gap: 1rem;
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  padding: 0.6rem 1.25rem;
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
}
.progress-bar-wrap {
  width: 140px;
  height: 8px;
  background: var(--border-color);
  border-radius: 999px;
  overflow: hidden;
}
.progress-bar-fill {
  width: 0%;
  height: 100%;
  background: linear-gradient(90deg, var(--primary), var(--secondary));
  transition: width 0.4s ease;
}
.progress-text {
  font-size: 0.85rem;
  font-weight: 700;
}

/* TABS NAVIGATION */
.tabs-nav-wrapper {
  background: var(--bg-surface);
  border-bottom: 1px solid var(--border-color);
  position: sticky;
  top: 57px;
  z-index: 40;
  backdrop-filter: blur(14px);
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.03);
}
.tabs-nav {
  max-width: 1200px;
  margin: 0 auto;
  display: flex;
  gap: 0.5rem;
  overflow-x: auto;
  scrollbar-width: none;
  padding: 0.65rem 1.5rem;
}
.tabs-nav::-webkit-scrollbar { display: none; }
.tab-btn {
  background: transparent;
  border: 1px solid transparent;
  padding: 0.65rem 1.15rem;
  border-radius: var(--radius-sm);
  font-family: 'Plus Jakarta Sans', sans-serif;
  font-size: 0.92rem;
  font-weight: 600;
  color: var(--text-muted);
  cursor: pointer;
  white-space: nowrap;
  transition: var(--transition);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}
.tab-btn:hover {
  color: var(--text-main);
  background: var(--primary-light);
}
.tab-btn.active {
  color: var(--primary);
  background: var(--primary-light);
  border-color: rgba(5, 150, 105, 0.3);
  font-weight: 700;
  box-shadow: 0 2px 8px rgba(5, 150, 105, 0.1);
}

/* MAIN CONTENT */
.main-content {
  max-width: 1200px;
  margin: 0 auto;
  padding: 2rem 1.5rem 4rem;
  flex: 1;
  width: 100%;
}
.tab-panel {
  display: none;
  animation: fadeIn 0.3s ease forwards;
}
.tab-panel.active {
  display: block;
}
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(6px); }
  to { opacity: 1; transform: translateY(0); }
}

/* CARDS */
.card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 1.75rem;
  margin-bottom: 1.5rem;
  box-shadow: var(--shadow-sm);
  transition: var(--transition);
}
.card:hover {
  box-shadow: var(--shadow-md);
}
.card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 1.25rem;
  padding-bottom: 0.75rem;
  border-bottom: 1px solid var(--border-color);
}
.card-title {
  font-family: 'Outfit', sans-serif;
  font-size: 1.35rem;
  font-weight: 700;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}
.card-badge {
  font-size: 0.75rem;
  font-weight: 700;
  padding: 0.2rem 0.6rem;
  border-radius: 999px;
  background: var(--primary-light);
  color: var(--primary);
}

/* ALERTS & CALLOUTS */
.alert-box {
  padding: 1.15rem 1.35rem;
  border-radius: var(--radius-md);
  margin: 1.25rem 0;
  font-size: 0.95rem;
  line-height: 1.65;
  display: block;
  border: 1px solid var(--border-color);
  border-left-width: 5px;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.03);
  transition: var(--transition);
}
.alert-box:hover {
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05);
}
.alert-title {
  font-weight: 700;
  font-size: 1rem;
  display: flex;
  align-items: center;
  gap: 0.45rem;
  margin-bottom: 0.45rem;
}
.alert-box p {
  margin: 0.35rem 0;
}
.alert-box p:first-child {
  margin-top: 0;
}
.alert-box p:last-child {
  margin-bottom: 0;
}
.alert-info { 
  background: var(--primary-light); 
  border-color: rgba(5, 150, 105, 0.25);
  border-left-color: var(--primary); 
}
.alert-info .alert-title { color: var(--primary); }
.alert-success { 
  background: var(--primary-light); 
  border-color: rgba(5, 150, 105, 0.25);
  border-left-color: var(--primary); 
}
.alert-warning { 
  background: var(--warning-light); 
  border-color: rgba(245, 158, 11, 0.25);
  border-left-color: var(--warning); 
}
.alert-warning .alert-title { color: #b45309; }
.alert-danger { 
  background: var(--danger-light); 
  border-color: rgba(239, 68, 68, 0.25);
  border-left-color: var(--danger); 
}
.alert-danger .alert-title { color: var(--danger); }

/* GRID */
.grid-2 {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 1.25rem;
}
.grid-3 {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 1.25rem;
}

/* FORMULAS */
.formula-box {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.2rem;
  text-align: center;
  font-size: 1.15rem;
  margin: 1rem 0;
  overflow-x: auto;
}

/* FORM CONTROLS & BUTTONS */
.form-group {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}
.form-label {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--text-muted);
}
.form-input {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 0.65rem 0.85rem;
  font-size: 1rem;
  color: var(--text-main);
  outline: none;
  transition: var(--transition);
}
.form-input:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px var(--primary-light);
}
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.4rem;
  font-weight: 700;
  font-size: 0.9rem;
  padding: 0.65rem 1.25rem;
  border-radius: var(--radius-sm);
  cursor: pointer;
  border: none;
  transition: var(--transition);
}
.btn-primary {
  background: var(--primary);
  color: #ffffff;
}
.btn-primary:hover {
  background: var(--primary-hover);
  transform: translateY(-1px);
}
.btn-outline {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  color: var(--text-main);
}
.btn-outline:hover {
  border-color: var(--primary);
  color: var(--primary);
}
.preset-buttons {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
  margin-bottom: 1.25rem;
}
.btn-preset {
  font-size: 0.78rem;
  padding: 0.3rem 0.75rem;
  border-radius: 999px;
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  cursor: pointer;
  color: var(--text-muted);
  transition: var(--transition);
}
.btn-preset:hover {
  border-color: var(--primary);
  color: var(--primary);
  background: var(--primary-light);
}

/* REAL NUMBER LINE CANVAS */
.line-canvas-container {
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 1.5rem;
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  min-height: 240px;
}
#numberLineCanvas {
  max-width: 100%;
  border-radius: var(--radius-sm);
  background: var(--bg-surface);
}

/* EXERCISE CARDS */
.exercise-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  margin-bottom: 1.25rem;
  transition: var(--transition);
}
.exercise-card.completed {
  border-color: var(--primary);
  background: linear-gradient(to right, var(--primary-light), transparent);
}
.ex-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0.75rem;
}
.ex-badge-level {
  font-size: 0.75rem;
  font-weight: 700;
  padding: 0.2rem 0.6rem;
  border-radius: 999px;
}
.badge-easy { background: var(--primary-light); color: var(--primary); }
.badge-med { background: var(--secondary-light); color: var(--secondary); }
.badge-hard { background: var(--danger-light); color: var(--danger); }
.ex-question {
  font-size: 1rem;
  font-weight: 600;
  margin-bottom: 1rem;
}
.ex-inputs {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
  align-items: center;
  margin-bottom: 0.75rem;
}
.ex-input {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 0.5rem 0.85rem;
  font-size: 0.95rem;
  color: var(--text-main);
  outline: none;
  min-width: 180px;
}
.ex-input:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px var(--primary-light);
}
.feedback-msg {
  font-size: 0.88rem;
  font-weight: 600;
  margin-top: 0.5rem;
  display: none;
}
.feedback-msg.show { display: block; }
.feedback-msg.correct { color: var(--primary); }
.feedback-msg.incorrect { color: var(--danger); }
.solution-collapsible {
  margin-top: 0.75rem;
  border-top: 1px dashed var(--border-color);
  padding-top: 0.75rem;
}
.details-toggle {
  background: none;
  border: none;
  color: var(--primary);
  font-size: 0.84rem;
  font-weight: 700;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.2rem 0;
}
.details-toggle:hover { text-decoration: underline; }
.solution-body {
  display: none;
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 1rem;
  margin-top: 0.5rem;
  font-size: 0.9rem;
}
.solution-body.open { display: block; }

/* EXAM ASSESSMENT */
.exam-header-banner {
  background: linear-gradient(135deg, rgba(2, 132, 199, 0.12), rgba(5, 150, 105, 0.12));
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  margin-bottom: 1.5rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 1rem;
}
.exam-score-display {
  font-size: 1.5rem;
  font-weight: 800;
  font-family: 'Outfit', sans-serif;
  color: var(--primary);
}

/* FOOTER */
.footer {
  margin-top: auto;
  border-top: 1px solid var(--border-color);
  background: var(--bg-card);
  padding: 1.5rem;
  text-align: center;
  color: var(--text-muted);
  font-size: 0.85rem;
}

/* RESPONSIVE */
@media (max-width: 640px) {
  .hero-title { font-size: 1.7rem; }
  .tabs-nav { padding: 0 0.75rem; }
  .tab-btn { padding: 0.85rem 0.9rem; font-size: 0.88rem; }
  .card { padding: 1.25rem; }
}