/* ============================================
   CSS CUSTOM PROPERTIES - Design System
   ============================================ */
:root {
  /* Colors */
  --color-primary: #6366f1;
  --color-primary-dark: #4f46e5;
  --color-success: #10b981;
  --color-success-dark: #059669;
  --color-danger: #ef4444;
  
  --color-text-primary: #111827;
  --color-text-secondary: #4b5563;
  --color-text-muted: #6b7280;
  
  --color-bg-primary: #ffffff;
  --color-bg-secondary: #f9fafb;
  --color-bg-tertiary: #f3f4f6;
  
  --color-border-light: #e5e7eb;
  --color-border-medium: #d1d5db;
  
  /* Spacing Scale */
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --space-2xl: 3rem;
  
  /* Typography */
  --font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen,
    Ubuntu, Cantarell, "Open Sans", "Helvetica Neue", sans-serif;
  --line-height-base: 1.6;
  --line-height-tight: 1.3;
  
  /* Borders & Radius */
  --border-radius-sm: 4px;
  --border-radius-md: 8px;
  --border-radius-lg: 12px;
  
  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
  
  /* Transitions */
  --transition-base: all 0.2s ease;
}

/* ============================================
   BASE STYLES
   ============================================ */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: var(--font-family);
  background-color: var(--color-bg-secondary);
  color: var(--color-text-primary);
  line-height: var(--line-height-base);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

main {
  flex: 1;
}

/* ============================================
   TYPOGRAPHY
   ============================================ */
h1, h2, h3, h4, h5, h6 {
  color: var(--color-text-primary);
  line-height: var(--line-height-tight);
  font-weight: 600;
  margin-bottom: var(--space-md);
}

h1 {
  font-size: 2.25rem;
  margin-top: var(--space-xl);
  margin-bottom: var(--space-lg);
}

h2 {
  font-size: 1.75rem;
  margin-top: var(--space-xl);
  padding-bottom: var(--space-sm);
  border-bottom: 2px solid var(--color-border-light);
}

h3 {
  font-size: 1.5rem;
  margin-top: var(--space-lg);
}

h4 {
  font-size: 1.25rem;
  margin-top: var(--space-lg);
}

p {
  margin-bottom: var(--space-md);
  color: var(--color-text-secondary);
}

a {
  color: var(--color-primary);
  text-decoration: none;
  transition: var(--transition-base);
}

a:hover {
  color: var(--color-primary-dark);
  text-decoration: underline;
}

.subtitle {
  font-size: 1.125rem;
  color: var(--color-text-muted);
  margin-bottom: var(--space-xl);
}

.module-title {
  color: var(--color-text-muted);
  font-size: 0.875rem;
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: var(--space-lg);
}

/* ============================================
   LAYOUT CONTAINERS
   ============================================ */
.container {
  max-width: 900px;
  margin: 0 auto;
  padding: var(--space-xl) var(--space-lg);
  background-color: var(--color-bg-primary);
}

/* ============================================
   NAVIGATION
   ============================================ */
.navbar {
  background-color: var(--color-bg-primary);
  border-bottom: 1px solid var(--color-border-light);
  box-shadow: var(--shadow-sm);
  position: sticky;
  top: 0;
  z-index: 1000;
}

.navbar .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-top: var(--space-md);
  padding-bottom: var(--space-md);
  background-color: transparent;
}

.logo {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-weight: 600;
  font-size: 1.125rem;
  color: var(--color-text-primary);
  text-decoration: none;
}

.logo:hover {
  text-decoration: none;
  color: var(--color-primary);
}

.logo img {
  width: 100px;
  height: auto;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: var(--space-lg);
}

.nav-links a {
  color: var(--color-text-secondary);
  font-weight: 500;
  text-decoration: none;
}

.nav-links a:hover {
  color: var(--color-primary);
  text-decoration: none;
}

.user-name {
  color: var(--color-text-muted);
  font-size: 0.875rem;
  padding: var(--space-sm) var(--space-md);
  background-color: var(--color-bg-tertiary);
  border-radius: var(--border-radius-md);
}

/* ============================================
   BUTTONS
   ============================================ */
.btn {
  display: inline-block;
  padding: 0.75rem 1.5rem;
  border-radius: var(--border-radius-md);
  font-weight: 500;
  text-align: center;
  cursor: pointer;
  transition: var(--transition-base);
  border: none;
  text-decoration: none;
  font-size: 1rem;
}

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

.btn-primary:hover {
  background-color: var(--color-success-dark);
  text-decoration: none;
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

.btn-secondary {
  background-color: var(--color-bg-tertiary);
  color: var(--color-text-secondary);
}

.btn-secondary:hover {
  background-color: var(--color-border-medium);
  text-decoration: none;
}

.btn-logout {
  background-color: var(--color-bg-secondary);
  color: var(--color-text-secondary);
  padding: var(--space-sm) var(--space-md);
  border-radius: var(--border-radius-md);
  font-size: 0.875rem;
}

.btn-logout:hover {
  background-color: var(--color-border-light);
  text-decoration: none;
}

/* ============================================
   COURSE GRID & CARDS
   ============================================ */
.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: var(--space-xl);
  margin-top: var(--space-xl);
  margin-bottom: var(--space-2xl);
}

.course-card {
  background-color: var(--color-bg-primary);
  border: 1px solid var(--color-border-light);
  border-radius: var(--border-radius-lg);
  padding: var(--space-xl);
  transition: var(--transition-base);
  box-shadow: var(--shadow-sm);
}

.course-card:hover {
  box-shadow: var(--shadow-lg);
  transform: translateY(-2px);
  border-color: var(--color-primary);
}

.course-card h3 {
  color: var(--color-text-primary);
  margin-top: 0;
  margin-bottom: var(--space-md);
  font-size: 1.25rem;
}

.course-card p {
  color: var(--color-text-secondary);
  margin-bottom: var(--space-lg);
  font-size: 0.9375rem;
}

.course-card .btn {
  width: 100%;
  margin-top: var(--space-md);
}

/* ============================================
   PROGRESS BAR
   ============================================ */
.progress-bar {
  width: 100%;
  height: 8px;
  background-color: var(--color-bg-tertiary);
  border-radius: var(--border-radius-md);
  overflow: hidden;
  margin-bottom: var(--space-sm);
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--color-success), var(--color-primary));
  transition: width 0.3s ease;
  border-radius: var(--border-radius-md);
}

.progress-text {
  font-size: 0.875rem;
  color: var(--color-text-muted);
  margin-bottom: var(--space-lg);
}

/* ============================================
   LESSON CONTENT
   ============================================ */
.lesson-content {
  background-color: var(--color-bg-primary);
  padding: var(--space-xl);
  border-radius: var(--border-radius-lg);
  margin-bottom: var(--space-xl);
  box-shadow: var(--shadow-sm);
}

.text-content {
  max-width: 100%;
}

.text-content ul {
  margin-left: var(--space-lg);
  margin-bottom: var(--space-lg);
}

.text-content li {
  margin-bottom: var(--space-sm);
  color: var(--color-text-secondary);
}

.text-content li strong {
  color: var(--color-text-primary);
}

/* ============================================
   CALLOUTS & SPECIAL BOXES
   ============================================ */
.callout {
  background-color: var(--color-bg-tertiary);
  border-left: 4px solid var(--color-primary);
  padding: var(--space-md) var(--space-lg);
  margin: var(--space-xl) 0;
  border-radius: var(--border-radius-sm);
}

.callout h3 {
  margin-top: 0;
  color: var(--color-text-primary);
}

.callout p:last-child {
  margin-bottom: 0;
}

/* Colored variants for different purposes */
div[style*="background: #f0fdf4"] {
  background-color: #f0fdf4 !important;
  border-left: 4px solid var(--color-success);
  padding: var(--space-md) var(--space-lg);
  border-radius: var(--border-radius-md);
  margin: var(--space-md) 0;
}

div[style*="background: #dbeafe"],
div[style*="background: #e0e7ff"] {
  background-color: #dbeafe !important;
  border-left: 4px solid var(--color-primary);
  padding: var(--space-md) var(--space-lg);
  border-radius: var(--border-radius-md);
  margin: var(--space-md) 0;
}

div[style*="background: #fef3c7"] {
  background-color: #fef3c7 !important;
  border-left: 4px solid #f59e0b;
  padding: var(--space-md) var(--space-lg);
  border-radius: var(--border-radius-md);
  margin: var(--space-md) 0;
}

div[style*="background: #fce7f3"] {
  background-color: #fce7f3 !important;
  border-left: 4px solid #ec4899;
  padding: var(--space-md) var(--space-lg);
  border-radius: var(--border-radius-md);
  margin: var(--space-md) 0;
}

div[style*="background: #dcfce7"] {
  background-color: #dcfce7 !important;
  border-left: 4px solid var(--color-success);
  padding: var(--space-md) var(--space-lg);
  border-radius: var(--border-radius-md);
  margin: var(--space-md) 0;
}

/* ============================================
   TABLES
   ============================================ */
table {
  width: 100%;
  border-collapse: collapse;
  margin: var(--space-xl) 0;
  background-color: var(--color-bg-primary);
  border-radius: var(--border-radius-md);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
}

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

th {
  background-color: var(--color-bg-tertiary);
  font-weight: 600;
  color: var(--color-text-primary);
}

td {
  color: var(--color-text-secondary);
}

tr:hover {
  background-color: var(--color-bg-secondary);
}

.comparison-table {
  width: 100%;
  border-collapse: collapse;
  margin: var(--space-xl) 0;
}

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

.comparison-table th {
  background-color: var(--color-bg-tertiary);
  font-weight: 600;
}

/* ============================================
   LESSON ACTIONS
   ============================================ */
.lesson-actions {
  display: flex;
  gap: var(--space-md);
  flex-wrap: wrap;
  margin-top: var(--space-xl);
  padding-top: var(--space-xl);
  border-top: 1px solid var(--color-border-light);
}

.lesson-actions form {
  flex: 1;
  min-width: 200px;
}

.lesson-actions .btn {
  width: 100%;
}

/* ============================================
   FOOTER
   ============================================ */
footer {
  background-color: var(--color-bg-tertiary);
  border-top: 1px solid var(--color-border-light);
  margin-top: auto;
  padding: var(--space-xl) 0;
}

footer .container {
  text-align: center;
  background-color: transparent;
  padding-top: var(--space-md);
  padding-bottom: var(--space-md);
}

footer p {
  color: var(--color-text-muted);
  font-size: 0.875rem;
  margin: 0;
}

/* ============================================
   RESPONSIVE DESIGN
   ============================================ */
@media (max-width: 768px) {
  :root {
    --space-xl: 1.5rem;
    --space-2xl: 2rem;
  }
  
  .container {
    padding: var(--space-md);
  }
  
  h1 {
    font-size: 1.875rem;
  }
  
  h2 {
    font-size: 1.5rem;
  }
  
  h3 {
    font-size: 1.25rem;
  }
  
  .navbar .container {
    flex-direction: column;
    gap: var(--space-md);
    align-items: flex-start;
  }
  
  .nav-links {
    width: 100%;
    justify-content: space-between;
  }
  
  .course-grid {
    grid-template-columns: 1fr;
    gap: var(--space-lg);
  }
  
  .lesson-actions {
    flex-direction: column;
  }
  
  .lesson-actions form,
  .lesson-actions .btn {
    width: 100%;
  }
}

@media (max-width: 480px) {
  .logo img {
    width: 80px;
  }
  
  .nav-links {
    flex-wrap: wrap;
    gap: var(--space-sm);
  }
  
  .user-name {
    font-size: 0.75rem;
    padding: var(--space-xs) var(--space-sm);
  }
}

/* ============================================
   UTILITY CLASSES
   ============================================ */
.text-center {
  text-align: center;
}

.text-muted {
  color: var(--color-text-muted);
}

.mt-xl {
  margin-top: var(--space-xl);
}

.mb-xl {
  margin-bottom: var(--space-xl);
}

.p-md {
  padding: var(--space-md);
}

.p-lg {
  padding: var(--space-lg);
}