.loading {
    display: none;
    width: 50px;
    height: 50px;
    border: 5px solid #f3f3f3;
    border-top: 5px solid #3498db;
    border-radius: 50%;
    animation: spin 1s linear infinite;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-top: -25px;
    margin-left: -25px;
  }
  
  @keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
  }