/* Button loader spinner */
  .loader {
    width: 16px;
    height: 16px;
    border: 2px solid rgba(255, 255, 255, 0.4);
    border-top-color: white;
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
  }

  .hidden {
    display: none;
  }

  @keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
  }

  @keyframes fadeInOut {
    0% { opacity: 0; transform: translateY(20px); }
    10% { opacity: 1; transform: translateY(0); }
    90% { opacity: 1; transform: translateY(0); }
    100% { opacity: 0; transform: translateY(20px); }
  }