/* CSS Variables */
:root {
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --secondary: #64748b;
  --success: #22c55e;
  --warning: #f59e0b;
  --danger: #ef4444;
  --dark: #1e293b;
  --light: #f8fafc;
  --gray-100: #f1f5f9;
  --gray-200: #e2e8f0;
  --gray-300: #cbd5e1;
  --gray-400: #94a3b8;
  --gray-500: #64748b;
  --gray-600: #475569;
  --gray-700: #334155;
  --gray-800: #1e293b;
  --sidebar-width: 280px;
  --header-height: 80px;
  --radius: 12px;
  --shadow: 0 1px 3px rgba(0,0,0,0.1), 0 1px 2px rgba(0,0,0,0.06);
  --shadow-lg: 0 10px 15px -3px rgba(0,0,0,0.1), 0 4px 6px -2px rgba(0,0,0,0.05);
}

/* Reset */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
  background: var(--gray-100);
  color: var(--gray-800);
  line-height: 1.6;
}

a {
  text-decoration: none;
  color: inherit;
}

/* Login Page */
.login-page {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
}

.login-container {
  background: white;
  padding: 3rem;
  border-radius: var(--radius);
  box-shadow: var(--shadow-lg);
  width: 100%;
  max-width: 420px;
}

.login-header {
  text-align: center;
  margin-bottom: 2rem;
}

.login-header h1 {
  font-size: 1.75rem;
  color: var(--gray-800);
  margin-bottom: 0.5rem;
}

.login-header p {
  color: var(--gray-500);
}

.form-group {
  margin-bottom: 1.5rem;
}

.form-group label {
  display: block;
  font-weight: 500;
  margin-bottom: 0.5rem;
  color: var(--gray-700);
}

.form-group input {
  width: 100%;
  padding: 0.875rem 1rem;
  border: 2px solid var(--gray-200);
  border-radius: 8px;
  font-size: 1rem;
  transition: border-color 0.2s, box-shadow 0.2s;
}

.form-group input:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.875rem 1.5rem;
  border-radius: 8px;
  font-weight: 600;
  font-size: 1rem;
  cursor: pointer;
  transition: all 0.2s;
  border: none;
}

.btn-primary {
  background: var(--primary);
  color: white;
  width: 100%;
}

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

.error-message {
  background: #fef2f2;
  color: var(--danger);
  padding: 0.75rem 1rem;
  border-radius: 8px;
  margin-bottom: 1rem;
  display: none;
  font-size: 0.875rem;
}

.error-message.show {
  display: block;
}

.demo-hint {
  text-align: center;
  margin-top: 1.5rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--gray-200);
  color: var(--gray-500);
  font-size: 0.875rem;
}

.demo-hint code {
  background: var(--gray-100);
  padding: 0.25rem 0.5rem;
  border-radius: 4px;
  font-family: monospace;
}

/* Dashboard Layout */
.dashboard-container {
  display: flex;
  min-height: 100vh;
}

/* Sidebar */
.sidebar {
  width: var(--sidebar-width);
  background: var(--gray-800);
  color: white;
  position: fixed;
  top: 0;
  left: 0;
  bottom: 0;
  display: flex;
  flex-direction: column;
  overflow-y: auto;
}

.sidebar-header {
  padding: 1.5rem;
  border-bottom: 1px solid var(--gray-700);
}

.logo {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  font-weight: 700;
  font-size: 1.125rem;
}

.logo svg {
  width: 24px;
  height: 24px;
  color: var(--primary);
}

.nav-menu {
  list-style: none;
  padding: 1rem 0;
  flex: 1;
}

.nav-section {
  padding: 1rem 1.5rem 0.5rem;
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--gray-400);
  font-weight: 600;
}

.nav-item {
  margin: 0.25rem 0.75rem;
}

.nav-link {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.75rem 1rem;
  border-radius: 8px;
  color: var(--gray-300);
  transition: all 0.2s;
  font-size: 0.9rem;
}

.nav-link:hover {
  background: var(--gray-700);
  color: white;
}

.nav-link.active {
  background: var(--primary);
  color: white;
}

.nav-link svg {
  width: 18px;
  height: 18px;
  flex-shrink: 0;
}

.sidebar-footer {
  padding: 1rem;
  border-top: 1px solid var(--gray-700);
}

.logout-btn {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  width: 100%;
  padding: 0.75rem 1rem;
  border-radius: 8px;
  background: transparent;
  border: 1px solid var(--gray-600);
  color: var(--gray-300);
  cursor: pointer;
  font-size: 0.9rem;
  transition: all 0.2s;
}

.logout-btn:hover {
  background: var(--gray-700);
  color: white;
}

.logout-btn svg {
  width: 18px;
  height: 18px;
}

/* Main Content */
.main-content {
  flex: 1;
  margin-left: var(--sidebar-width);
  padding: 2rem;
}

.content-header {
  margin-bottom: 2rem;
}

.content-header h1 {
  font-size: 1.75rem;
  color: var(--gray-800);
  margin-bottom: 0.5rem;
}

.content-header .subtitle {
  color: var(--gray-500);
}

/* Course Grid */
.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 1.5rem;
}

.course-card {
  background: white;
  border-radius: var(--radius);
  padding: 1.5rem;
  box-shadow: var(--shadow);
  transition: all 0.2s;
  border: 1px solid var(--gray-200);
}

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

.course-card-header {
  display: flex;
  align-items: flex-start;
  gap: 1rem;
  margin-bottom: 1rem;
}

.course-icon {
  width: 48px;
  height: 48px;
  background: linear-gradient(135deg, var(--primary), var(--primary-dark));
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  flex-shrink: 0;
}

.course-icon svg {
  width: 24px;
  height: 24px;
}

.course-card h3 {
  font-size: 1.125rem;
  color: var(--gray-800);
  margin-bottom: 0.25rem;
}

.course-card p {
  color: var(--gray-500);
  font-size: 0.9rem;
  line-height: 1.5;
}

.course-card-footer {
  margin-top: 1.5rem;
  padding-top: 1rem;
  border-top: 1px solid var(--gray-100);
}

.course-link {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--primary);
  font-weight: 600;
  font-size: 0.9rem;
}

.course-link:hover {
  color: var(--primary-dark);
}

.course-link svg {
  width: 16px;
  height: 16px;
}

/* Video Grid */
.video-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 1.5rem;
}

.video-card {
  background: white;
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow);
  transition: all 0.2s;
  border: 1px solid var(--gray-200);
}

.video-card:hover {
  box-shadow: var(--shadow-lg);
  transform: translateY(-2px);
}

.video-thumbnail {
  aspect-ratio: 16/9;
  background: linear-gradient(135deg, var(--gray-200), var(--gray-300));
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
}

.video-thumbnail svg {
  width: 48px;
  height: 48px;
  color: var(--gray-400);
}

.video-placeholder-text {
  position: absolute;
  bottom: 0.75rem;
  right: 0.75rem;
  background: rgba(0,0,0,0.6);
  color: white;
  padding: 0.25rem 0.5rem;
  border-radius: 4px;
  font-size: 0.75rem;
}

.video-info {
  padding: 1rem 1.25rem;
}

.video-info h3 {
  font-size: 1rem;
  color: var(--gray-800);
  margin-bottom: 0.25rem;
}

.video-info p {
  color: var(--gray-500);
  font-size: 0.85rem;
}

.video-duration {
  margin-top: 0.5rem;
  font-size: 0.8rem;
  color: var(--gray-400);
}

/* Stats Section */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1rem;
  margin-bottom: 2rem;
}

.stat-card {
  background: white;
  padding: 1.25rem;
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  border: 1px solid var(--gray-200);
}

.stat-card h4 {
  color: var(--gray-500);
  font-size: 0.85rem;
  font-weight: 500;
  margin-bottom: 0.5rem;
}

.stat-card .value {
  font-size: 1.75rem;
  font-weight: 700;
  color: var(--gray-800);
}

/* Course View (iframe wrapper) */
.course-frame-container {
  background: white;
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow);
  border: 1px solid var(--gray-200);
}

.course-frame {
  width: 100%;
  height: calc(100vh - 180px);
  border: none;
}

/* Responsive */
@media (max-width: 1024px) {
  .sidebar {
    transform: translateX(-100%);
    z-index: 1000;
    transition: transform 0.3s;
  }

  .sidebar.open {
    transform: translateX(0);
  }

  .main-content {
    margin-left: 0;
  }

  .mobile-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 1rem;
    background: white;
    border-bottom: 1px solid var(--gray-200);
    margin: -2rem -2rem 2rem;
  }

  .menu-toggle {
    background: none;
    border: none;
    cursor: pointer;
    padding: 0.5rem;
  }

  .menu-toggle svg {
    width: 24px;
    height: 24px;
    color: var(--gray-700);
  }
}

@media (max-width: 640px) {
  .login-container {
    margin: 1rem;
    padding: 2rem;
  }

  .course-grid,
  .video-grid {
    grid-template-columns: 1fr;
  }
}