■プログレスバー:progress::基本的な使用例

 <div class="progress mb-3">
    <div class="progress-bar" role="progressbar" aria-valuenow="0" aria-valuemin="0" aria-valuemax="100"></div>
  </div>
  <div class="progress mb-3">
    <div class="progress-bar" style="width: 20%" role="progressbar" aria-valuenow="25" aria-valuemin="0" aria-valuemax="100"></div>
  </div>
  <div class="progress mb-3">
    <div class="progress-bar w-50" role="progressbar" aria-valuenow="50" aria-valuemin="0" aria-valuemax="100"></div>
  </div>
  <div class="progress mb-3">
    <div class="progress-bar" style="width: 80%" role="progressbar" aria-valuenow="75" aria-valuemin="0" aria-valuemax="100"></div>
  </div>
  <div class="progress">
    <div class="progress-bar w-100" role="progressbar" aria-valuenow="100" aria-valuemin="0" aria-valuemax="100"></div>
  </div>