2. CSS tùy chỉnh cho Modal (popup) ​

 <style>

  .modal {

    display: none;

    position: fixed;

    z-index: 50;

    left: 0;

    top: 0;

    width: 100%;

    height: 100%;

    overflow: auto;

    background: rgba(0, 0, 0, 0.7);

    align-items: center;

    justify-content: center;

  }

  .modal-content {

    background: white;

    margin: auto;

    padding: 20px;

    border-radius: 8px;

    max-width: 90%;

    width: 600px;

    box-shadow: 0 5px 15px rgba(0,0,0,0.3);

    position: relative;

  }

  .close-button {

    color: #aaa;

    position: absolute;

    top: 10px;

    right: 15px;

    font-size: 28px;

    font-weight: bold;

    cursor: pointer;

  }

  .close-button:hover {

    color: black;

  }

</style>​