: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: #0d9488;
  --primary-hover: #0f766e;
  --primary-light: #f0fdfa;
  --secondary: #6366f1;
  --secondary-light: #eef2ff;
  --accent: #0284c7;
  --accent-light: #f0f9ff;
  --success: #10b981;
  --success-light: #ecfdf5;
  --warning: #f59e0b;
  --warning-light: #fffbeb;
  --danger: #ef4444;
  --danger-light: #fef2f2;
  --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(13, 148, 136, 0.18);
  --transition: all 0.22s ease;
}

[data-theme="dark"] {
  --bg-main: #061e1b;
  --bg-surface: #0a2925;
  --bg-card: rgba(10, 41, 37, 0.92);
  --border-color: rgba(20, 83, 76, 0.7);
  --text-main: #f8fafc;
  --text-muted: #94a3b8;
  --primary: #2dd4bf;
  --primary-hover: #5eead4;
  --primary-light: rgba(45, 212, 191, 0.15);
  --secondary: #818cf8;
  --secondary-light: rgba(129, 140, 248, 0.15);
  --accent: #38bdf8;
  --accent-light: rgba(56, 189, 248, 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);
  transform: translateX(-2px);
}
.nav-title {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-family: 'Outfit', sans-serif;
  font-weight: 700;
  font-size: 1.05rem;
}
.nav-badge {
  background: var(--primary-light);
  color: var(--primary);
  padding: 0.15rem 0.55rem;
  border-radius: 999px;
  font-size: 0.75rem;
  font-weight: 700;
}
.theme-btn {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  color: var(--text-main);
  padding: 0.45rem 0.75rem;
  border-radius: 999px;
  cursor: pointer;
  font-size: 0.95rem;
  transition: var(--transition);
}
.theme-btn:hover {
  border-color: var(--primary);
  transform: scale(1.05);
}

/* HERO */
.hero {
  background: linear-gradient(135deg, rgba(13, 148, 136, 0.1) 0%, rgba(99, 102, 241, 0.08) 100%);
  border-bottom: 1px solid var(--border-color);
  padding: 2.5rem 1.5rem 2rem;
}
.hero-container {
  max-width: 1200px;
  margin: 0 auto;
}
.hero-pill {
  display: inline-block;
  background: var(--primary-light);
  color: var(--primary);
  font-weight: 700;
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  padding: 0.25rem 0.75rem;
  border-radius: 999px;
  margin-bottom: 0.75rem;
}
.hero-title {
  font-family: 'Outfit', sans-serif;
  font-size: 2.3rem;
  font-weight: 800;
  line-height: 1.2;
  margin-bottom: 0.6rem;
  background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}
.hero-subtitle {
  color: var(--text-muted);
  font-size: 1.05rem;
  max-width: 780px;
  margin-bottom: 1.25rem;
}
.progress-summary {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  padding: 0.5rem 1rem;
  border-radius: 999px;
  width: fit-content;
  box-shadow: var(--shadow-sm);
}
.progress-bar-wrap {
  width: 130px;
  height: 8px;
  background: var(--border-color);
  border-radius: 999px;
  overflow: hidden;
}
.progress-bar-fill {
  height: 100%;
  width: 0%;
  background: linear-gradient(90deg, var(--primary), var(--secondary));
  transition: width 0.4s ease;
}
.progress-text {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--primary);
}

/* TABS NAVIGATION */
.tabs-nav-wrapper {
  background: var(--bg-surface);
  border-bottom: 1px solid var(--border-color);
  position: sticky;
  top: 57px;
  z-index: 40;
}
.tabs-nav {
  max-width: 1200px;
  margin: 0 auto;
  display: flex;
  gap: 0.5rem;
  padding: 0.5rem 1.5rem;
  overflow-x: auto;
}
.tab-btn {
  background: transparent;
  border: 1px solid transparent;
  color: var(--text-muted);
  font-family: 'Outfit', sans-serif;
  font-size: 0.92rem;
  font-weight: 700;
  padding: 0.5rem 1.1rem;
  border-radius: 999px;
  cursor: pointer;
  white-space: nowrap;
  transition: var(--transition);
}
.tab-btn:hover {
  color: var(--text-main);
  background: var(--bg-main);
}
.tab-btn.active {
  background: var(--primary);
  color: #fff;
  box-shadow: 0 2px 8px rgba(13, 148, 136, 0.25);
}

/* MAIN CONTENT */
.main-content {
  max-width: 1200px;
  margin: 0 auto;
  padding: 2.5rem 1.5rem 4rem;
  flex: 1;
  width: 100%;
}
.tab-panel {
  display: none;
}
.tab-panel.active {
  display: block;
  animation: fadeIn 0.25s ease forwards;
}
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(6px); }
  to { opacity: 1; transform: translateY(0); }
}

/* CARDS */
.card {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  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: 1rem;
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 0.75rem;
}
.card-title {
  font-family: 'Outfit', sans-serif;
  font-size: 1.3rem;
  font-weight: 700;
  color: var(--text-main);
  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);
}

/* GRIDS */
.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;
}

/* FORMULA BOX */
.formula-box {
  background: var(--bg-main);
  border-left: 4px solid var(--primary);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  padding: 1rem 1.25rem;
  margin: 1rem 0;
  font-size: 0.95rem;
}

/* EXERCISE CARD */
.exercise-card {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  margin-bottom: 1.25rem;
  box-shadow: var(--shadow-sm);
  transition: var(--transition);
}
.exercise-card.completed {
  border-color: var(--success);
  background: linear-gradient(to right, var(--bg-surface), var(--success-light));
}
.exercise-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0.75rem;
}
.exercise-title {
  font-family: 'Outfit', sans-serif;
  font-size: 1.1rem;
  font-weight: 700;
}
.exercise-status-badge {
  font-size: 0.78rem;
  font-weight: 700;
  padding: 0.15rem 0.6rem;
  border-radius: 999px;
  background: var(--border-color);
  color: var(--text-muted);
}
.exercise-card.completed .exercise-status-badge {
  background: var(--success);
  color: #fff;
}
.exercise-input-group {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  margin-top: 1rem;
  flex-wrap: wrap;
}
.input-answer {
  background: var(--bg-main);
  border: 1px solid var(--border-color);
  color: var(--text-main);
  padding: 0.5rem 0.85rem;
  border-radius: var(--radius-sm);
  font-size: 1rem;
  font-weight: 600;
  min-width: 140px;
  outline: none;
  transition: var(--transition);
}
.input-answer:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px var(--primary-light);
}
.btn-check {
  background: var(--primary);
  color: #fff;
  border: none;
  padding: 0.5rem 1.1rem;
  border-radius: var(--radius-sm);
  font-weight: 700;
  font-size: 0.88rem;
  cursor: pointer;
  transition: var(--transition);
}
.btn-check:hover {
  background: var(--primary-hover);
  transform: translateY(-1px);
}
.btn-hint {
  background: transparent;
  color: var(--text-muted);
  border: 1px solid var(--border-color);
  padding: 0.5rem 0.85rem;
  border-radius: var(--radius-sm);
  font-size: 0.88rem;
  font-weight: 600;
  cursor: pointer;
  transition: var(--transition);
}
.btn-hint:hover {
  border-color: var(--text-muted);
  color: var(--text-main);
}
.feedback-box {
  margin-top: 0.85rem;
  padding: 0.75rem 1rem;
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  display: none;
}
.feedback-box.show {
  display: block;
}
.feedback-success {
  background: var(--success-light);
  color: var(--success);
  border: 1px solid var(--success);
}
.feedback-error {
  background: var(--danger-light);
  color: var(--danger);
  border: 1px solid var(--danger);
}
.hint-text {
  margin-top: 0.6rem;
  font-size: 0.88rem;
  color: var(--text-muted);
  display: none;
  background: var(--bg-main);
  padding: 0.6rem 0.9rem;
  border-radius: var(--radius-sm);
}

/* SIMULATOR STYLES */
.sim-container {
  background: var(--bg-main);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  margin-top: 1rem;
}
.sim-controls {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1rem;
  margin-bottom: 1.25rem;
}
.sim-control-item label {
  display: block;
  font-size: 0.85rem;
  font-weight: 700;
  margin-bottom: 0.35rem;
  color: var(--text-muted);
}
.sim-control-item input[type="range"] {
  width: 100%;
  accent-color: var(--primary);
}
.sim-canvas-wrap {
  width: 100%;
  height: 320px;
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  position: relative;
  overflow: hidden;
  display: flex;
  align-items: center;
  justify-content: center;
}
.sim-results {
  margin-top: 1rem;
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 1rem;
  font-family: 'Fira Code', monospace;
  font-size: 0.92rem;
}

/* TEST QUIZ */
.quiz-item {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  margin-bottom: 1.25rem;
}
.quiz-question {
  font-weight: 700;
  margin-bottom: 1rem;
  font-size: 1.05rem;
}
.quiz-options {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}
.quiz-option-label {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.65rem 1rem;
  background: var(--bg-main);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: var(--transition);
  font-size: 0.92rem;
}
.quiz-option-label:hover {
  border-color: var(--primary);
}
.quiz-option-label.correct {
  border-color: var(--success);
  background: var(--success-light);
  color: var(--success);
  font-weight: 700;
}
.quiz-option-label.wrong {
  border-color: var(--danger);
  background: var(--danger-light);
  color: var(--danger);
}

/* FOOTER */
footer {
  margin-top: auto;
  border-top: 1px solid var(--border-color);
  background: var(--bg-surface);
  padding: 2rem 1.5rem;
  text-align: center;
  font-size: 0.88rem;
  color: var(--text-muted);
}