body {
    font-family: Arial, sans-serif;
    padding: 20px;
    background: #f4f4f4;
  }
  
  h1 {
    text-align: center;
    color: #333;
  }
  
  form, .invoice {
    background: white;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
    margin-bottom: 20px;
  }
  
  input, textarea, select {
    width: 100%;
    padding: 8px;
    margin: 8px 0 16px;
    box-sizing: border-box;
    border: 1px solid #ccc;
    border-radius: 5px;
  }
  
  button {
    background: #4CAF50;
    color: white;
    padding: 10px 15px;
    border: none;
    border-radius: 5px;
    cursor: pointer;
  }
  
  button:hover {
    background: #45a049;
  }
  
  table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 20px;
  }
  
  table, th, td {
    border: 1px solid #ddd;
  }
  
  th, td {
    padding: 12px;
    text-align: left;
  }
  
  .hidden {
    display: none;
  }