Bootstrap Example</title>

  <meta charset="utf-8">

  <meta name="viewport" content="width=device-width, initial-scale=1">

  <link href="https://cdn.jsdelivr.net/npm/bootstrap@5.1.1/dist/css/bootstrap.min.css" rel="stylesheet">

  <script src="https://cdn.jsdelivr.net/npm/bootstrap@5.1.1/dist/js/bootstrap.bundle.min.js"></script>

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<div class="container mt-3">

  <h3>水平和垂直方向都居中显示</h3>

  <p>点击按钮打开模态框</p>

  <button type="button" class="btn btn-primary" data-bs-toggle="modal" data-bs-target="#myModal">

    打开模态框

  </button>

</div>

<!-- 模态框 -->

<div class="modal" id="myModal">