.slider-container {
    justify-content: center;
    display: flex;
    align-items: center;
    gap: 20px;
  }
  button.nav-btn {
    font-size: 2rem;
    background: none;
    border: none;
    cursor: pointer;
    user-select: none;
    padding: 0 10px;
    color: #333;
    transition: color 0.3s;
  }
  button.nav-btn:hover {
    color: #0082F3;
  }
  .card {
    width: 320px;
    height: 420px;
    perspective: 1000px;
    cursor: pointer;
    position: relative;
  }
  .card-inner {
    position: relative;
    width: 100%;
    height: 100%;
    transition: transform 0.6s;
    transform-style: preserve-3d;
    border-radius: 12px;
    box-shadow: 0 6px 15px rgba(0,0,0,0.1);
    background-color: #fff;
  }
  .card.flipped .card-inner {
    transform: rotateY(180deg);
  }
  .card-front, .card-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: 12px;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    padding: 30px;
    box-sizing: border-box;
  }
  .card-back img {
    max-width: 80%;
    max-height: 180px;
    object-fit: contain;
    margin-bottom: 20px;
    border-radius: 10px;
    box-shadow: 0 4px 8px rgba(0,0,0,0.2);
    user-select: none;
    pointer-events: none;
  }
  
  .card-front {
    border: 2.5px solid #69b9ff;
    /* background-color: #e0f7fa; */
    background-color: #fff;
    font-size: 8rem;
    font-weight: bold;
    /* color: #00796b; */
    color: black;
    user-select: none;
  }
  .card-back {
    /* background-color: #00796b; */
    background: linear-gradient(180deg, #8992ED 0%, #1B2592 100%);
    color: white;
    transform: rotateY(180deg);
    font-size: 1.5rem;
    text-align: center;
    user-select: none;
  }
  .word {
    font-weight: 700;
    font-size: 2.5rem;
    margin-bottom: 10px;
  }
  .transcription {
    font-style: italic;
    font-size: 1.3rem;
    margin-bottom: 30px;
  }
  button.audio-btn {
    background-color: #fff;
    border: 1px solid #111;
    padding: 10px 20px;
    border-radius: 6px;
    color: #111;
    font-size: 1rem;
    cursor: pointer;
    transition: background-color 0.6s;
  }
  button.audio-btn:hover {
    background-color: #69b9ff;
  }
  .progress {
    text-align: center;
    margin-top: 25px;
    font-size: 1.1rem;
    color: #555;
  }
  @media (max-width: 400px) {
    .card {
      width: 260px;
      height: 340px;
    }
    .card-front {
      font-size: 6rem;
    }
    .word {
      font-size: 2rem;
    }
  }
  

  

  .card-front, .card-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: 12px;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    padding: 30px;
    box-sizing: border-box;
    user-select: none;
  }
  
  #letter-text {
    font-size: 8rem;
    font-weight: bold;
    color: black;
    margin-bottom: 20px;
  }
  
  .audio-btn {
    background-color: #fff;
    border: none;
    padding: 10px 20px;
    border-radius: 6px;
    color: #111;
    font-size: 1rem;
    cursor: pointer;
    transition: background-color 0.6s;
    user-select: none;
  }
  
  .audio-btn:hover {
    background-color: #69b9ff;
  }
  

  /* .speed-control {
    margin-top: 15px;
    font-size: 1rem;
    color: #333;
    user-select: none;
    display: flex;
    align-items: center;
    gap: 10px;
    justify-content: center;
  }
  
  #speedRange {
    width: 150px;
  }
   */