<div class="container">
  <div class="row">
    <div class="col my-3">
      <ol class="level">
        <li>はじめに
          <ol class="level">
            <li>研究の背景</li>
            <li>研究の目的</li>
          </ol>
        </li>
        <li>準備</li>
        <li>本論
          <ol class="level">
            <li>問題提起</li>
            <li>研究の説明</li>
          </ol>
        </li>
        <li>考察</li>
        <li>結論</li>
      </ol>
    </div>
  </div>
</div>
ol.level {
  counter-reset: item;
  li {
    display: block;
  }
  li:before {
    content: counters(item, "-") ". ";
    counter-increment: item;
  }
}
View Compiled

External CSS

  1. https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css
  2. https://stackpath.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css

External JavaScript

  1. https://code.jquery.com/jquery-3.3.1.slim.min.js
  2. https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js
  3. https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js