body {
  margin: 0;
  font-family: 'Poppins', sans-serif;
  background: var(--bg);
  color: var(--text);
  transition: background 0.3s, color 0.3s;
}
:root {
  --bg: #ffffff;
  --text: #111111;
  --card-bg: #f5f5f5;
  --shadow: rgba(0, 0, 0, 0.1);
}
body.dark {
  --bg: #121212;
  --text: #f0f0f0;
  --card-bg: #1e1e1e;
  --shadow: rgba(255, 255, 255, 0.05);
}
header {
  padding: 1rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  background: linear-gradient(90deg, #6dd5ed, #2193b0);
  color: white;
}
#subjects {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1rem;
  padding: 1rem;
}
.subject-card {
  background: var(--card-bg);
  padding: 1rem;
  border-radius: 1rem;
  box-shadow: 0 4px 6px var(--shadow);
  transition: transform 0.2s;
}
.subject-card:hover {
  transform: scale(1.03);
}
button {
  padding: 0.5rem 1rem;
  border: none;
  border-radius: 0.5rem;
  background: #4facfe;
  color: white;
  font-weight: bold;
  cursor: pointer;
}
button:hover {
  background: #00f2fe;
}
.modal {
  position: fixed;
  top: 0; left: 0;
  width: 100%; height: 100%;
  background: rgba(0,0,0,0.5);
  display: flex;
  justify-content: center;
  align-items: center;
}
.modal-content {
  background: var(--bg);
  padding: 2rem;
  border-radius: 1rem;
  box-shadow: 0 4px 12px var(--shadow);
}
.hidden { display: none; }
.loader {
  border: 6px solid #f3f3f3;
  border-top: 6px solid #3498db;
  border-radius: 50%;
  width: 40px;
  height: 40px;
  animation: spin 1s linear infinite;
  margin: 2rem auto;
}
@keyframes spin {
  0% { transform: rotate(0deg); }
  100% { transform: rotate(360deg); }
}
.offline {
  text-align: center;
  padding: 1rem;
  background: #ff6b6b;
  color: white;
}