body {
    font-family: system-ui, -apple-system, sans-serif;
    max-width: 600px;
    margin: 2rem auto;
    padding: 0 1rem;
  }
  
  h1 {
    margin-bottom: 0.25rem;
  }
  
  #message {
    width: 100%;
    font-size: 1.25rem;
    padding: 0.5rem;
    margin: 1rem 0;
    box-sizing: border-box;
  }
  
  .grid {
    display: grid;
    grid-template-columns: repeat(6, 1fr);
    grid-template-rows: repeat(6, 1fr);
    gap: 6px;
    width: 100%;
    max-width: 600px;
    aspect-ratio: 1;
  }
  
  .cell {
    aspect-ratio: 1;
    border: 1px solid #333;
    background: #ffffff;
    overflow: hidden;
  }
  
  .cell img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    display: block;
  }
  
  .cell {
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2rem;
    font-weight: bold;
  }

  .cell {
    cursor: pointer;
  }
  
  .cell:empty,
  .cell:not(:has(img)) {
    cursor: default;
  }

  #download {
    margin-top: 1rem;
    padding: 0.6rem 1rem;
    font-size: 1rem;
    cursor: pointer;
  }
  
  .cell.space {
    background: #f5f5f5;
    border-style: dashed;
  }