:root {
  --primary-color: #4f46e5;
  --secondary-color: #f8fafc;
  --bg-dark: #0f172a;
  --bg-light: #ffffff;
  --text-dark: #0f172a;
  --text-light: #f1f5f9;
}

body {
  margin: 0;
  font-family: 'Segoe UI', sans-serif;
  background-color: var(--secondary-color);
  color: var(--text-dark);
  transition: background 0.3s, color 0.3s;
}

.dark-mode {
  background-color: var(--bg-dark);
  color: var(--text-light);
}

.theme-toggle {
  position: fixed;
  top: 1rem;
  right: 1rem;
  background: var(--primary-color);
  border: none;
  padding: 0.5rem;
  border-radius: 50%;
  color: white;
  cursor: pointer;
  z-index: 1000;
}

.site-title {
  font-size: 1.8rem;
  font-weight: bold;
}

.live-class {
  background-color: #1e293b;
  border-radius: 12px;
}

.subject-card {
  background-color: #e2e8f0;
  border-left: 5px solid var(--primary-color);
  transition: transform 0.3s, background-color 0.3s;
}

.subject-card:hover {
  transform: translateY(-5px);
  background-color: #cbd5e1;
}

.dark-mode .subject-card {
  background-color: #334155;
  color: var(--text-light);
}

footer {
  font-size: 1rem;
}

.custom-header {
  background: #e0f2fe;
}

.dark-mode .custom-header {
  background: #1e293b;
}

.sub-heading-section {
  background-color: #f1f5f9;
  padding: 2rem;
  border-radius: 12px;
}

.dark-mode .sub-heading-section {
  background-color: #1e293b;
}

.sidebar {
  position: fixed;
  top: 0;
  right: -300px;
  width: 300px;
  height: 100%;
  background-color: #ffffff;
  box-shadow: -2px 0 5px rgba(0,0,0,0.5);
  padding: 1rem;
  transition: right 0.3s ease;
  z-index: 999;
}

.dark-mode .sidebar {
  background-color: #1e293b;
  color: var(--text-light);
}

.sidebar.show {
  right: 0;
}

.close-btn {
  background: none;
  border: none;
  font-size: 1.5rem;
  float: right;
  cursor: pointer;
}



.video-section {
      display: none;
      padding: 2rem;
}

.video-container {
      width: 100%;
      max-width: 800px;
      aspect-ratio: 16/9;
      margin: auto;
      overflow: hidden;
      border-radius: 10px;
      border: 4px solid var(--primary-color);
      box-shadow: 0 0 15px rgba(0, 0, 0, 0.2);
      background-color: white;
}