body {
    margin: 0;
    font-family: Arial, sans-serif;
    background: #f4f4f4;
  }
  
  header {
    background: #1976d2;
    color: white;
    text-align: center;
    padding: 20px;
  }
  
  nav {
    background: #eeeeee;
  }
  
  nav ul {
    display: flex;
    justify-content: center;
    list-style: none;
    padding: 10px;
    margin: 0;
    gap: 20px;
  }
  
  nav a {
    text-decoration: none;
    color: #333;
    font-weight: bold;
  }
  
  nav a:hover {
    color: #1976d2;
  }
  
  main {
    max-width: 800px;
    margin: 30px auto;
  }
  
  .box {
    background: white;
    padding: 20px;
    margin: 20px auto;
    max-width: 800px;
    border-radius: 10px;
    box-shadow: 0 4px 10px rgba(0,0,0,0.1);
  }
  
  button {
    padding: 10px 20px;
    border: none;
    border-radius: 5px;
    background: #1976d2;
    color: white;
    cursor: pointer;
  }
  
  button:hover {
    background: #0d47a1;
  }
  
  footer {
    text-align: center;
    padding: 15px;
    background: #ddd;
  }
  
  .normal {
    color: black;
  }
  
  .henkou {
    color: red;
    font-size: 24px;
  }
  
  #square {
    width: 100px;
    height: 100px;
    background: #ccffb2;
    margin: 10px auto;
  }
  
  #message {
    margin-top: 15px;
    font-size: 18px;
    color: #1976d2;
    opacity: 0;
    transition: opacity 0.5s;
  }