* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
  }
  
  body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: #f9f9f9;
    color: #333;
    line-height: 1.6;
    padding: 20px;
  }
  
  header {
    text-align: center;
    margin-bottom: 30px;
  }
  
  header h1 {
    font-size: 2.2rem;
    color: #2e7d32;
  }
  
  header p {
    color: #666;
  }
  
  main {
    max-width: 600px;
    margin: 0 auto;
  }
  
  button {
    display: block;
    width: 100%;
    padding: 14px;
    margin: 10px 0;
    font-size: 1.1rem;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    transition: background 0.3s;
  }
  
  #btn2d {
    background: #4CAF50;
    color: white;
  }
  
  #btn2d:hover {
    background: #388E3C;
  }
  
  #btn3d {
    background: #2196F3;
    color: white;
  }
  
  #btn3d:hover {
    background: #0b7dda;
  }
  
  #btn-calcular {
    background: #FF9800;
    color: white;
  }
  
  #btn-calcular:hover {
    background: #EF6C00;
  }
  
  #btn-volver {
    background: #9E9E9E;
    color: white;
  }
  
  #btn-volver:hover {
    background: #757575;
  }
  
  #form-section, #btn-volver {
    text-align: center;
  }
  
  select, input {
    width: 100%;
    padding: 10px;
    margin: 8px 0;
    border: 1px solid #ccc;
    border-radius: 6px;
    font-size: 1rem;
  }
  
  #result {
    margin-top: 20px;
    padding: 15px;
    background: #e8f5e9;
    border-left: 4px solid #4CAF50;
    border-radius: 4px;
    display: none;
  }
  
  footer {
    text-align: center;
    margin-top: 40px;
    color: #888;
    font-size: 0.9rem;
  }
  footer img{
    margin-top: 30px;
  }
  
  @media (max-width: 600px) {
    body {
      padding: 10px;
    }
  }