body {
    margin: 0;
    height: 100vh;
    background: #0e0e0e;
    font-family: -apple-system, BlinkMacSystemFont, sans-serif;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    color: white;
  }
  
  .deck {
    position: relative;
    width: 280px;
    height: 400px;
  }
  
  .card, .stack {
    position: absolute;
    width: 100%;
    height: 100%;
    border-radius: 18px;
  }
  
  /* 메인 카드 */
  .card {
    transform-style: preserve-3d;
    transition: transform 0.6s;
    z-index: 3;
  }
  
  .card.flip {
    transform: rotateY(180deg);
  }
  
  .card div {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: 18px;
    padding: 24px;
    box-sizing: border-box;
    display: flex;
    flex-direction: column;
    justify-content: center;
    text-align: center;
  }
  
  /* 카드 앞면 */
  .front {
    background: #f7f7f7;
    color: #111;
    transform: rotateY(180deg);
  }
  
  .front p {
    font-size: 20px;
    margin-bottom: 20px;
  }
  
  .front span {
    font-size: 14px;
    color: #e63946;
    font-weight: bold;
  }
  
  /* 카드 뒷면 */
  .back {
    background: linear-gradient(135deg, #333, #111);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 28px;
    font-weight: bold;
  }
  
  /* 쌓인 카드 효과 */
  .stack {
    background: #222;
  }
  
  .stack1 {
    transform: translateY(6px) scale(0.98);
    z-index: 2;
  }
  
  .stack2 {
    transform: translateY(12px) scale(0.96);
    z-index: 1;
  }
  
  /* NEXT 버튼 */
  #nextBtn {
    margin-top: 40px;
    padding: 14px 36px;
    font-size: 18px;
    border-radius: 30px;
    border: none;
    background: #ffffff;
    cursor: pointer;
  }