body {
  font-family: 'Segoe UI', sans-serif;
  margin: 0;
  background: #f5f5f5;
  color: #222;
}

header, footer {
  background: #1e1e1e;
  color: #fff;
  padding: 15px 20px;
  text-align: center;
}

header a {
  color: #fff;
  font-size: 24px;
  text-decoration: none;
}

main {
  padding: 20px;
}

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: 12px;
  padding: 20px;
}
.card {
  aspect-ratio: 1 / 1;
  border-radius: 10px;
  background: var(--card-bg);
  overflow: hidden;
  box-shadow: 0 2px 6px var(--card-shadow);
  transition: transform 0.2s ease;
  display: block;
}
.card:hover {
  transform: scale(1.03);
}
.card img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  display: block;
}

.card h3 {
  font-size: 15px;
  margin: 6px 0 2px;
  text-align: center;
  color: #111;
}

.card p {
  font-size: 12px;
  color: #555;
  text-align: center;
  margin: 0;
}

footer {
  font-size: 14px;
}

.lesson-frame iframe {
  width: 100%;
  height: 90vh;
  border: none;
}

:root {
  --bg-color: #f5f5f5;
  --text-color: #222;
  --card-bg: #fff;
  --card-shadow: rgba(0, 0, 0, 0.1);
  --button-bg: #444;
  --button-text: #fff;
}

body.dark {
  --bg-color: #1c1c1c;
  --text-color: #eaeaea;
  --card-bg: #2c2c2c;
  --card-shadow: rgba(0, 0, 0, 0.4);
  --button-bg: #ddd;
  --button-text: #111;
}

body {
  background: var(--bg-color);
  color: var(--text-color);
}

.card, .description-box, .related-grid .card {
  background: var(--card-bg);
  box-shadow: 0 2px 6px var(--card-shadow);
}

button#toggleTheme {
  background: var(--button-bg) !important;
  color: var(--button-text) !important;
}

@media screen and (max-width: 768px) {
  .nomobile {
    visibility: hidden;
    display: none;
  }
 
}