body {
  font-family: system-ui, sans-serif;
  padding: 2rem;
}

.section {
  margin-top: 2rem;
}

.hidden {
  display: none;
}

.course-grid {
  margin-top: 1rem;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 1rem;
}

.course-card {
  background: white;
  padding: 1rem;
  border-radius: 10px;
  box-shadow: 0 4px 10px rgba(0,0,0,0.1);
}

.course-card.completed {
  background: #d8f5d8;
  border-left: 6px solid #2e8b57;
}

.course-id {
  font-weight: 700;
}

.course-name {
  margin: 0.5rem 0;
}

.course-credits {
  opacity: 0.8;
  font-size: 0.9rem;
}

.toggle-btn {
  margin-top: 0.75rem;
  padding: 0.5rem 0.75rem;
  border: 0;
  border-radius: 8px;
  cursor: pointer;
}

.course-card.locked {
  opacity: 0.55;
  filter: grayscale(0.2);
}

.course-card.locked .course-name,
.course-card.locked .course-credits,
.course-card.locked .course-id {
  opacity: 0.9;
}

.toggle-btn:disabled {
  cursor: not-allowed;
  opacity: 0.7;
}

.missing-prereqs {
  margin-top: 0.5rem;
  font-size: 0.85rem;
  opacity: 0.85;
}