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                <!DOCTYPE html>
      .center {
          margin: 0 auto;
          width: 50%;
          border: 2px solid red;
          padding: 15px;

      <h2>Căn giữa cho phần tử</h2>
      <p>Để căn giữa theo chiều ngang cho một phần tử khối (như div) bạn có thể sử 
dụng margin: 0 auto.</p>

      <div class="center">
        <p><b>Note: </b>Đây là ví dụ cho thấy phần tử được căn giữa bằng thuộc tính margin: 0 auto, với chiều rộng là 50% ,khoảng cách trên dưới trái phải là 15px,...</p>