* {
    box-sizing: border-box;
  }
  body {
    margin: 0;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Arial, sans-serif;
    background: #f8fafc;
    color: #0f172a;
  }
  .topbar {
    background: #1e293b;
    color: white;
    padding: 16px 20px;
    display: flex;
    justify-content: space-between;
    align-items: center;
  }
  .brand {
    font-size: 20px;
    font-weight: bold;
  }
  .brand span {
    color: #38bdf8;
  }
  .secure-badge {
    background: #0ea5e9;
    padding: 6px 14px;
    border-radius: 999px;
    font-size: 13px;
    font-weight: bold;
  }
  .main {
    padding: 30px 15px;
  }
  .checkout {
    max-width: 700px;
    margin: auto;
    background: white;
    padding: 30px;
    border-radius: 16px;
    box-shadow: 0 4px 20px rgba(15, 23, 42, 0.08);
  }
  .checkout-header {
    margin-bottom: 25px;
  }
  .eyebrow {
    color: #0284c7;
    font-weight: bold;
    text-transform: uppercase;
    font-size: 12px;
    margin: 0 0 6px;
  }
  h1 {
    margin: 0 0 8px;
    font-size: 28px;
  }
  .checkout-header p {
    color: #64748b;
    margin: 0;
    font-size: 15px;
    line-height: 1.5;
  }
  .section-title {
    font-weight: bold;
    margin: 20px 0 15px;
    color: #334155;
    border-bottom: 1px solid #e2e8f0;
    padding-bottom: 6px;
  }
  .info-text {
    font-size: 14px;
    color: #475569;
    line-height: 1.5;
    background: #f0f9ff;
    padding: 12px;
    border-left: 4px solid #0ea5e9;
    border-radius: 4px;
    margin-bottom: 20px;
  }
  .grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 15px;
  }
  .field {
    margin-bottom: 15px;
  }
  label {
    display: block;
    font-weight: 600;
    margin-bottom: 6px;
    font-size: 14px;
  }
  input {
    width: 100%;
    padding: 12px;
    border: 1px solid #cbd5e1;
    border-radius: 8px;
    font-size: 15px;
    outline: none;
    transition: 0.2s;
  }
  input:focus {
    border-color: #0ea5e9;
    box-shadow: 0 0 0 3px #e0f2fe;
  }
  input.invalid {
    border-color: #ef4444;
    background: #fef2f2;
  }
  small {
    color: #ef4444;
    font-size: 12px;
    display: block;
    margin-top: 4px;
    min-height: 15px;
  }
  button {
    width: 100%;
    padding: 14px;
    border: none;
    border-radius: 8px;
    background: #0ea5e9;
    color: white;
    font-size: 16px;
    font-weight: bold;
    cursor: pointer;
    margin-top: 10px;
    transition: 0.2s;
  }
  button:hover {
    background: #0284c7;
  }
  #btn-confirmar-codigo {
    background: #10b981;
  }
  #btn-confirmar-codigo:hover {
    background: #059669;
  }
  .resultado {
    margin-top: 20px;
    padding: 15px;
    border-radius: 8px;
    font-weight: bold;
    text-align: center;
  }
  .resultado.ok {
    background: #ecfdf5;
    color: #065f46;
    border: 1px solid #a7f3d0;
  }
  .resultado.error {
    background: #fef2f2;
    color: #991b1b;
    border: 1px solid #fca5a5;
  }
  .hidden {
    display: none;
  }
  @media (max-width: 550px) {
    .grid {
      grid-template-columns: 1fr;
    }
  }