:root {
  /* Colors */
  --primary-color: #4f46e5; /* Indigo */
  --primary-hover: #4338ca;
  --secondary-color: #64748b;
  --success-color: #10b981;
  --warning-color: #f59e0b;
  --danger-color: #ef4444;
  
  --bg-body: #f3f4f6;
  --bg-card: #ffffff;
  --bg-sidebar: #1e293b;
  
  --text-main: #111827;
  --text-muted: #6b7280;
  --text-light: #f3f4f6;

  --border-color: #e5e7eb;
  
  /* Role Specific Accents */
  --admin-accent: #4f46e5;
  --teacher-accent: #059669;
  --student-accent: #d97706;

  /* Spacing */
  --spacing-xs: 0.25rem;
  --spacing-sm: 0.5rem;
  --spacing-md: 1rem;
  --spacing-lg: 1.5rem;
  --spacing-xl: 2rem;

  /* Radius */
  --radius-sm: 0.25rem;
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
}

* {
  box-sizing: border-box;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background-color: var(--bg-body);
  color: var(--text-main);
  margin: 0;
  line-height: 1.5;
}

h1, h2, h3, h4, h5, h6 {
  margin-top: 0;
  color: var(--text-main);
}

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

/* Layout */
.layout {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

.sidebar {
  width: 100%;
  background-color: var(--bg-sidebar);
  color: var(--text-light);
  flex-shrink: 0;
  display: flex;
  flex-direction: column;
}

.sidebar-header {
  padding: var(--spacing-lg);
  font-size: 1.25rem;
  font-weight: bold;
  border-bottom: 1px solid rgba(255,255,255,0.1);
}

.sidebar-nav {
  padding: var(--spacing-md);
  flex-grow: 1;
}

.nav-item {
  display: block;
  padding: var(--spacing-sm) var(--spacing-md);
  color: #cbd5e1;
  border-radius: var(--radius-md);
  margin-bottom: var(--spacing-xs);
  transition: all 0.2s;
}

.nav-item:hover, .nav-item.active {
  background-color: rgba(255,255,255,0.1);
  color: white;
}

.main-content {
  flex-grow: 1;
  padding: var(--spacing-xl);
  overflow-y: auto;
}

.header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: var(--spacing-xl);
}

.user-profile {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
}

.avatar {
  width: 40px;
  height: 40px;
  background-color: var(--primary-color);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-weight: bold;
}

/* Components */
.panel-gray {
  background-color: #f9fafb;
  padding: var(--spacing-lg);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  margin-top: var(--spacing-md);
}

.card {
  background-color: var(--bg-card);
  border-radius: var(--radius-lg);
  padding: var(--spacing-lg);
  box-shadow: 0 1px 3px rgba(0,0,0,0.1);
  margin-bottom: var(--spacing-lg);
}

.grid-3 {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--spacing-lg);
}

.grid-2 {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--spacing-lg);
}

.stat-card {
  display: flex;
  flex-direction: column;
}

.stat-value {
  font-size: 2rem;
  font-weight: bold;
  color: var(--text-main);
}

.stat-label {
  color: var(--text-muted);
  font-size: 0.875rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  padding: var(--spacing-sm) var(--spacing-md);
  border-radius: var(--radius-md);
  font-weight: 500;
  cursor: pointer;
  border: 1px solid transparent;
  transition: background-color 0.2s;
}

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

.btn-secondary {
  background-color: white;
  border-color: var(--border-color);
  color: var(--text-main);
}
.btn-secondary:hover {
  background-color: #f9fafb;
}

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

.table-container {
  overflow-x: auto;
}

.table {
  width: 100%;
  border-collapse: collapse;
  text-align: left;
}

.table th {
  background-color: #f9fafb;
  padding: var(--spacing-md);
  font-weight: 600;
  color: var(--text-muted);
  border-bottom: 1px solid var(--border-color);
}

.table td {
  padding: var(--spacing-md);
  border-bottom: 1px solid var(--border-color);
}

.badge {
  display: inline-block;
  padding: 0.25rem 0.5rem;
  border-radius: 9999px;
  font-size: 0.75rem;
  font-weight: 600;
}

.badge-success {
  background-color: #d1fae5;
  color: #065f46;
}

.badge-warning {
  background-color: #fef3c7;
  color: #92400e;
}

.badge-primary {
  background-color: #e0e7ff;
  color: #3730a3;
}

.alert {
  padding: var(--spacing-md);
  border-radius: var(--radius-md);
  margin-bottom: var(--spacing-md);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.alert-success {
  background-color: #d1fae5;
  color: #065f46;
  border: 1px solid #a7f3d0;
}

.form-group {
  margin-bottom: var(--spacing-md);
}

.form-label {
  display: block;
  margin-bottom: var(--spacing-xs);
  font-weight: 500;
  color: var(--text-main);
}

.form-input, .form-select, .form-textarea {
  width: 100%;
  padding: var(--spacing-sm);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  font-size: 1rem;
}

.form-textarea {
  min-height: 100px;
}

/* Landing Page Specific */
.landing-container {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
  background: linear-gradient(135deg, #4f46e5 0%, #06b6d4 100%);
}

.login-card {
  background: white;
  padding: var(--spacing-xl);
  border-radius: var(--radius-lg);
  width: 100%;
  max-width: 400px;
  box-shadow: 0 10px 25px rgba(0,0,0,0.1);
}

.role-selector {
  display: flex;
  justify-content: center;
  gap: var(--spacing-sm);
  margin-bottom: var(--spacing-lg);
}

.role-btn {
  padding: var(--spacing-sm);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  cursor: pointer;
  opacity: 0.7;
}

.role-btn.active {
  opacity: 1;
  border-color: var(--primary-color);
  background-color: #eff6ff;
  color: var(--primary-color);
}

/* Role Theming Overrides */
.theme-admin .sidebar { background-color: #1e1b4b; } /* Dark indigo */
.theme-teacher .sidebar { background-color: #064e3b; } /* Dark green */
.theme-student .sidebar { background-color: #78350f; } /* Dark orange/brown */

.theme-admin .btn-primary { background-color: var(--admin-accent); }
.theme-teacher .btn-primary { background-color: var(--teacher-accent); }
.theme-student .btn-primary { background-color: var(--student-accent); }

/* Course Player */
.course-layout {
  display: grid;
  grid-template-columns: 1fr;
  min-height: 100vh;
}
.player-sidebar {
  background: white;
  border-right: none;
  border-bottom: 1px solid var(--border-color);
  display: flex;
  flex-direction: column;
  max-height: 300px; /* Mobile: Scrollable short list */
  overflow-y: auto;
}
.player-content {
  padding: var(--spacing-xl);
  background: var(--bg-body);
  overflow-y: auto;
}
.module-header {
  padding: 1rem;
  background: #f9fafb;
  font-weight: bold;
  border-bottom: 1px solid var(--border-color);
  border-top: 1px solid var(--border-color);
}
.lesson-item {
  padding: 0.75rem 1rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  cursor: pointer;
  border-bottom: 1px solid var(--border-color);
  color: var(--text-muted);
}
.lesson-item:hover {
  background-color: #f3f4f6;
}
.lesson-item.active {
  background-color: #fff7ed;
  color: var(--student-accent);
  border-left: 3px solid var(--student-accent);
}
.lesson-item.completed {
  text-decoration: line-through;
  opacity: 0.7;
}
.video-placeholder {
  width: 100%;
  aspect-ratio: 16/9;
  background-color: black;
  margin-bottom: 1.5rem;
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-size: 1.5rem;
}

/* Toolbar & Utilities */
.toolbar {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
  margin-bottom: var(--spacing-md);
}

.search-input {
  width: 100%;
}

/* Desktop Responsive Styles */
@media (min-width: 1200px) {
  /* Layout: Switch back to row for desktop */
  .layout {
    flex-direction: row;
  }

  /* Sidebar: Fixed width on left */
  .sidebar {
    width: 280px;
    height: 100vh;
    position: sticky;
    top: 0;
    overflow-y: auto;
  }

  /* Main Content: Add more breathing room */
  .main-content {
    padding: var(--spacing-xl) 3rem; /* More horizontal padding */
    max-width: 1600px;
    margin: 0 auto;
  }

  /* Header: Larger text */
  .header h2 {
    font-size: 2rem;
  }

  /* Grid Systems: Multi-column restore */
  .grid-3 {
    grid-template-columns: repeat(3, 1fr);
    gap: 2rem;
  }

  .grid-2 {
    grid-template-columns: repeat(2, 1fr);
    gap: 2rem;
  }

  /* Toolbar: Row layout on desktop */
  .toolbar {
    flex-direction: row;
    justify-content: space-between;
    align-items: center;
  }

  .search-input {
    width: 350px;
  }

  /* Course Player: Side-by-side */
  .course-layout {
    grid-template-columns: 350px 1fr;
  }

  .player-sidebar {
    height: 100vh;
    max-height: none; /* Restore full height */
    position: sticky;
    top: 0;
    overflow-y: auto;
    border-right: 1px solid var(--border-color);
    border-bottom: none;
  }
  
  /* Tables: Better spacing */
  .table th, .table td {
    padding: 1rem 1.5rem;
  }
  
  /* Typography Scale Up */
  body {
    font-size: 1rem; /* Ensure base size is good */
  }
}