body {
  margin-bottom: 60px;
  /* prevent content from hiding behind footer */
}

.option-card {
  border-radius: 1rem;
  overflow: hidden;
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.15);
  transition: transform 0.2s ease-in-out;
}

.option-card:hover {
  transform: scale(1.03);
}

.option-card img {
  height: 250px;
  object-fit: cover;
}

.option-card .card-body {
  text-align: center;
}

.option-card .btn {
  font-size: 1.2rem;
  padding: 0.75rem 1.5rem;
}

.flashcard {
  width: 250px;
  height: 350px;
  perspective: 1000px;
  cursor: pointer;
  margin: auto;
}

.flashcard-inner {
  width: 100%;
  height: 100%;
  transition: transform 0.6s;
  transform-style: preserve-3d;
  position: relative;
}

.flashcard.flipped .flashcard-inner {
  transform: rotateY(180deg);
}

.flashcard-front,
.flashcard-back {
  position: absolute;
  width: 100%;
  height: 100%;
  backface-visibility: hidden;
  border: 2px solid #333;
  border-radius: 12px;
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
  padding: 20px;
}

.flashcard-front {
  background: #f9f9f9;
}

.flashcard-back {
  background: #4CAF50;
  color: white;
  transform: rotateY(180deg);
}

#options .btn {
  width: 100%;
  font-size: 1.2rem;
  padding: 10px;
}

#chartTitle {
  font-size: 2rem;
  font-weight: bold;
  text-align: center;
  margin: 20px 0;
}

#chartTable td {
  width: 80px;
  height: 80px;
  vertical-align: middle;
  text-align: center;
  font-size: 1.1rem;
}

#chartTable strong {
  font-size: 2rem;
  display: block;
  margin-bottom: 5px;
}

#chartTable div:last-child {
  font-size: 1rem;
}

footer {
  background: #f8f9fa;
  padding: 15px 0;
  margin-top: 40px;
  text-align: center;
  font-size: 0.9rem;
  color: #6c757d;
}