.flashcard-container {
  perspective: 1000px;
}

#flashcard {
  transition: transform 0.6s;
  transform-style: preserve-3d;
}

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

.front,
.back {
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
}

.back {
  transform: rotateY(180deg);
}

/* 自定义模态框样式 */
#addCardModal {
  display: none;
  align-items: center;
  justify-content: center;
}

#addCardModal.hidden {
  display: none !important;
}

.modal-content {
  background: white;
  padding: 2rem;
  border-radius: 0.5rem;
  width: 90%;
  max-width: 500px;
}

.progress-bar {
  height: 8px;
  background: #e0e0e0;
  border-radius: 4px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: #4caf50;
  transition: width 0.3s ease;
}