.subject-nav-section {
  background-color: var(--off-white);
  padding: 20px 0;
  border-bottom: 1px solid var(--border-color);
}

.subject-nav {
  display: flex;
  justify-content: center;
  align-items: center;
  flex-wrap: wrap;
  gap: 15px;
}

.chapter-grid-section {
  padding: 40px 0;
}

.chapter-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 30px;
}

.chapter-card {
  background-color: #fff;
  border: 1px solid var(--border-color);
  border-radius: var(--border-radius);
  box-shadow: 0 4px 6px rgba(0, 0, 0, 0.04);
  padding: 30px;
  display: flex;
  flex-direction: column;
  transition: transform 0.3s ease, box-shadow 0.3s ease;
  border-top: 4px solid var(--secondary-color);
}

.chapter-card:hover {
  transform: translateY(-8px);
  box-shadow: var(--shadow);
  border-top-color: var(--primary-color);
}

.chapter-card h3 {
  color: var(--dark-blue);
  font-size: 1.5rem;
  margin-bottom: 15px;
  font-weight: 600;
}

.chapter-card p {
  color: var(--text-color);
  margin-bottom: 25px;
  flex-grow: 1;
}

.chapter-card .btn {
  width: 100%;
}

@media (max-width: 768px) {
  .chapter-grid {
    grid-template-columns: 1fr;
  }

  .subject-nav {
    gap: 10px;
  }
  .subject-nav-section {
  padding: 15px 0;
}
.chapter-grid-section {
  padding: 20px 0;
}
}