* {
    box-sizing: border-box;
  }
  
  html, body {
    margin: 0;
    padding: 0;
    width: 100%;
    overflow-x: hidden;
    background: #ffffff;
    font-family: 'Segoe UI', sans-serif;
  }
  
  h2 {
    color: #FFA500;
    font-size: 24px;
    margin-bottom: 6px;
  }
  
  h3 {
    color: #FFA500;
    margin-bottom: 16px;
    font-weight: 500;
    font-size: 16px;
  }
  
  label {
    font-weight: bold;
    color: #FFA500;
    display: block;
    margin-top: 14px;
    font-size: 14px;
  }
  
  .input-icon {
    position: relative;
    margin-bottom: 16px;
  }
  
  .input-icon i {
    position: absolute;
    top: 50%;
    left: 12px;
    transform: translateY(-50%);
    color: #ff9900;
    pointer-events: none;
  }
  
  .input-icon input {
    padding-left: 40px;
  }
  
  input, select {
    width: 100%;
    padding: 12px;
    margin-top: 6px;
    border: 1px solid #ffaa00aa;
    background: #fff;
    color: #111;
    font-size: 16px;
    border-radius: 10px;
    outline: none;
    box-shadow: inset 0 0 4px #00000022;
    transition: border-color 0.3s ease, transform 0.2s ease;
  }
  
  input:focus, select:focus {
    border-color: #ff6600;
    transform: scale(1.01);
  }
  
  input::placeholder {
    color: #999;
  }
  
  input:disabled {
    background: #eee;
    color: #666;
  }
  
  button {
    background: linear-gradient(to right, #FFA500, #FF7F00);
    color: white;
    border: none;
    padding: 14px;
    font-size: 16px;
    border-radius: 10px;
    cursor: pointer;
    width: 100%;
    font-weight: bold;
    box-shadow: 0 4px 8px #00000033;
    transition: transform 0.2s, background 0.3s;
  }
  
  button:hover {
    background: linear-gradient(to right, #FF7F00, #FFA500);
    transform: scale(1.02);
  }
  
  #mensaje {
    margin-top: 20px;
    color: #00c98d;
    font-weight: bold;
    text-align: center;
    font-size: 16px;
  }
  
  .formulario-container {
    width: 100%;
    max-width: 100%;
    margin: 0;
    padding: 20px;
    background: transparent;
    border-radius: 0;
    box-shadow: none;
  }
  
  .input-group-responsive {
    display: flex;
    flex-direction: column;
    gap: 12px;
  }
  
  @media (min-width: 600px) {
    .formulario-container {
      max-width: 480px;
      margin: auto;
      background: #ffffffee;
      border-radius: 18px;
      box-shadow: 0 0 20px #00000022;
    }
  
    .input-group-responsive {
      flex-direction: row;
    }
  }
  
  .oculto {
    display: none;
  }
  
  .spinner {
    display: inline-block;
    width: 16px;
    height: 16px;
    border: 3px solid rgba(255, 255, 255, 0.3);
    border-top-color: #fff;
    border-radius: 50%;
    animation: girar 0.8s linear infinite;
    vertical-align: middle;
    margin-right: 8px;
  }
  
  @keyframes girar {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
  }
  
  /* BONUS: efecto visual para botón desactivado */
  button:disabled {
    opacity: 0.6;
    cursor: not-allowed;
  }