/* Data Analytics Active Learning Platform - Clean & Modern Styling */
:root {
  --primary: #009688;
  --primary-dark: #00796b;
  --primary-light: #e0f2f1;
  --primary-hover: #00897b;
  
  --secondary: #1e293b;
  --secondary-light: #f1f5f9;
  
  --accent: #f59e0b;
  --accent-light: #fef3c7;
  
  --success: #10b981;
  --success-bg: #ecfdf5;
  --success-border: #a7f3d0;
  
  --danger: #ef4444;
  --danger-bg: #fef2f2;
  --danger-border: #fecaca;
  
  --info: #3b82f6;
  --info-bg: #eff6ff;

  --bg-main: #f8fafc;
  --bg-card: #ffffff;
  --bg-subtle: #f8fafc;
  --text-main: #0f172a;
  --text-muted: #64748b;
  --border-color: #e2e8f0;
  
  --shadow-sm: 0 1px 3px 0 rgb(0 0 0 / 0.07);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1);
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
}

[data-theme="dark"] {
  --bg-main: #0b1329;
  --bg-card: #151f38;
  --bg-subtle: #1e294b;
  --text-main: #f8fafc;
  --text-muted: #94a3b8;
  --border-color: #27355a;
  --primary-light: #0d3835;
  --success-bg: #064e3b;
  --success-border: #059669;
  --danger-bg: #450a0a;
  --danger-border: #991b1b;
  --info-bg: #172554;
  --accent-light: #451a03;
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

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

/* Header */
.app-header {
  background-color: var(--bg-card);
  border-bottom: 1px solid var(--border-color);
  padding: 0.85rem 1.5rem;
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: var(--shadow-sm);
}

.header-container {
  max-width: 1100px;
  margin: 0 auto;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.brand-badge {
  background: linear-gradient(135deg, var(--primary), var(--primary-dark));
  color: white;
  padding: 0.35rem 0.75rem;
  border-radius: var(--radius-sm);
  font-weight: 800;
  font-size: 0.85rem;
  letter-spacing: 0.5px;
}

.brand-title {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--text-main);
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.55rem 1.1rem;
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  border: 1px solid transparent;
  transition: var(--transition);
  user-select: none;
}

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

.btn-primary:hover {
  background-color: var(--primary-hover);
  transform: translateY(-1px);
}

.btn-outline {
  background-color: transparent;
  border-color: var(--border-color);
  color: var(--text-main);
}

.btn-outline:hover {
  background-color: var(--bg-subtle);
}

.btn-sm {
  padding: 0.35rem 0.75rem;
  font-size: 0.82rem;
}

.btn-accent {
  background-color: var(--accent);
  color: white;
}

/* Nav Bar / Selector */
.topic-nav {
  background-color: var(--bg-card);
  border-bottom: 1px solid var(--border-color);
  padding: 0.75rem 1.5rem;
}

.topic-nav-container {
  max-width: 1100px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 1rem;
}

.filter-select {
  padding: 0.55rem 1rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  background-color: var(--bg-main);
  color: var(--text-main);
  font-size: 0.95rem;
  font-weight: 600;
  outline: none;
  cursor: pointer;
  min-width: 320px;
}

.filter-select:focus {
  border-color: var(--primary);
}

.stats-pill {
  display: inline-flex;
  align-items: center;
  gap: 0.75rem;
  background-color: var(--bg-subtle);
  padding: 0.4rem 0.9rem;
  border-radius: 20px;
  border: 1px solid var(--border-color);
  font-size: 0.85rem;
  font-weight: 600;
}

/* Main Content */
.main-content {
  max-width: 1100px;
  margin: 1.5rem auto;
  padding: 0 1.5rem;
  width: 100%;
  flex: 1;
}

/* Question Card */
.study-card {
  background-color: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 2rem;
  box-shadow: var(--shadow-md);
  margin-bottom: 2rem;
}

.card-top {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1.25rem;
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 0.85rem;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.badge-group {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex-wrap: wrap;
}

.badge {
  font-size: 0.75rem;
  font-weight: 700;
  padding: 0.25rem 0.6rem;
  border-radius: 4px;
  text-transform: uppercase;
}

.badge-part {
  background-color: var(--secondary);
  color: white;
}

.badge-theme {
  background-color: var(--primary-light);
  color: var(--primary);
}

.progress-text {
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--text-muted);
}

.question-heading {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--text-main);
  margin-bottom: 1.5rem;
  line-height: 1.5;
}

/* Options */
.options-grid {
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
  margin-bottom: 1.5rem;
}

.option-item {
  display: flex;
  align-items: flex-start;
  gap: 1rem;
  padding: 1.1rem 1.25rem;
  background-color: var(--bg-main);
  border: 2px solid var(--border-color);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: var(--transition);
  text-align: left;
  font-size: 1rem;
  color: var(--text-main);
  width: 100%;
}

.option-item:hover:not(.locked) {
  border-color: var(--primary);
  background-color: var(--primary-light);
  transform: translateX(4px);
}

.option-letter {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 30px;
  height: 30px;
  border-radius: 50%;
  background-color: var(--bg-card);
  border: 1px solid var(--border-color);
  font-weight: 700;
  font-size: 0.85rem;
  flex-shrink: 0;
}

.option-item.correct {
  border-color: var(--success);
  background-color: var(--success-bg);
  color: var(--text-main);
}

.option-item.correct .option-letter {
  background-color: var(--success);
  color: white;
  border-color: var(--success);
}

.option-item.incorrect {
  border-color: var(--danger);
  background-color: var(--danger-bg);
  color: var(--text-main);
}

.option-item.incorrect .option-letter {
  background-color: var(--danger);
  color: white;
  border-color: var(--danger);
}

.option-item.locked {
  cursor: default;
}

/* Theory & Explanation Card (The Core Learning Module) */
.theory-module {
  background-color: var(--bg-subtle);
  border: 1px solid var(--border-color);
  border-left: 5px solid var(--primary);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  margin-top: 1.5rem;
  display: none;
  animation: slideDown 0.3s ease-out;
}

.theory-module.show {
  display: block;
}

.theory-banner {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-size: 1.1rem;
  font-weight: 800;
  margin-bottom: 1rem;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--border-color);
}

.theory-banner.correct {
  color: var(--success);
}

.theory-banner.incorrect {
  color: var(--danger);
}

.theory-section {
  margin-bottom: 1.25rem;
}

.theory-section h4 {
  font-size: 0.95rem;
  color: var(--primary-dark);
  margin-bottom: 0.4rem;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.theory-section p, .theory-section ul {
  font-size: 0.95rem;
  color: var(--text-main);
  line-height: 1.6;
}

.theory-section ul {
  margin-left: 1.5rem;
  margin-top: 0.5rem;
}

.theory-section li {
  margin-bottom: 0.4rem;
}

.pitfall-box {
  background-color: var(--accent-light);
  border-left: 4px solid var(--accent);
  padding: 0.75rem 1rem;
  border-radius: var(--radius-sm);
  margin: 0.85rem 0;
  font-size: 0.9rem;
}

.summary-card-inner {
  background-color: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 1rem;
  margin-top: 0.75rem;
}

/* Tables inside Theory */
.summary-table {
  width: 100%;
  border-collapse: collapse;
  margin: 0.75rem 0;
  font-size: 0.85rem;
}

.summary-table th, .summary-table td {
  padding: 0.5rem 0.75rem;
  border: 1px solid var(--border-color);
  text-align: left;
}

.summary-table th {
  background-color: var(--bg-subtle);
  font-weight: 700;
}

/* Code Snippets */
pre, code {
  font-family: Consolas, Monaco, "Courier New", monospace;
  font-size: 0.9rem;
  background-color: var(--bg-subtle);
  padding: 0.2rem 0.4rem;
  border-radius: 4px;
}

pre {
  padding: 0.75rem;
  margin: 0.5rem 0;
  overflow-x: auto;
}

/* Controls */
.action-controls {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 1.5rem;
  flex-wrap: wrap;
  gap: 1rem;
}

@keyframes slideDown {
  from { opacity: 0; transform: translateY(-8px); }
  to { opacity: 1; transform: translateY(0); }
}

@media (max-width: 768px) {
  .study-card {
    padding: 1.25rem;
  }
  .filter-select {
    min-width: 100%;
  }
}