h1, h2, h3, h4, h5, h6,
.h1, .h2, .h3, .h4, .h5, .h6 {
  margin-bottom: 0.5rem;
  font-family: inherit;
  font-weight: 500;
  line-height: 1.2;
  color: inherit;
}

h1, .h1 {
  font-size: 2.5rem;
}

h2, .h2 {
  font-size: 2rem;
}

h3, .h3 {
  font-size: 1.75rem;
}

h4, .h4 {
  font-size: 1.5rem;
}

h5, .h5 {
  font-size: 1.25rem;
}

h6, .h6 {
  font-size: 1rem;
}

<p class="h1">h1. Bootstrap heading</p>
<p class="h2">h2. Bootstrap heading</p>
<p class="h3">h3. Bootstrap heading</p>
<p class="h4">h4. Bootstrap heading</p>
<p class="h5">h5. Bootstrap heading</p>
<p class="h6">h6. Bootstrap heading</p>

<h3>Fancy display heading <small class="text-muted">With faded secondary text</small></h3>

<h1 class="display-1">Display 1</h1>
<h1 class="display-2">Display 2</h1>
<h1 class="display-3">Display 3</h1>
<h1 class="display-4">Display 4</h1>

.display-1 {
  font-size: 6rem;
  font-weight: 300;
  line-height: 1.2;
}

.display-2 {
  font-size: 5.5rem;
  font-weight: 300;
  line-height: 1.2;
}

.display-3 {
  font-size: 4.5rem;
  font-weight: 300;
  line-height: 1.2;
}

.display-4 {
  font-size: 3.5rem;
  font-weight: 300;
  line-height: 1.2;
}

.lead {
  font-size: 1.25rem;
  font-weight: 300;
}

<p class="lead">
  Vivamus sagittis lacus vel augue laoreet rutrum faucibus dolor auctor. Duis mollis, est non commodo luctus.
</p>

<p>You can use the mark tag to <mark>highlight</mark> text.</p>
<p><del>This line of text is meant to be treated as deleted text.</del></p>
<p><s>This line of text is meant to be treated as no longer accurate.</s></p>
<p><ins>This line of text is meant to be treated as an addition to the document.</ins></p>
<p><u>This line of text will render as underlined</u></p>
<p><small>This line of text is meant to be treated as fine print.</small></p>
<p><strong>This line rendered as bold text.</strong></p>
<p><em>This line rendered as italicized text.</em></p>

<p><abbr title="attribute">attr</abbr></p>
<p><abbr title="HyperText Markup Language" class="initialism">HTML</abbr> is fun!</p>

<blockquote class="blockquote">
  <p class="mb-0">Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante.</p>
</blockquote>

<blockquote class="blockquote">
  <p class="mb-0">Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante.</p>
  <footer class="blockquote-footer">Someone famous in <cite title="Source Title">Source Title</cite></footer>
</blockquote>

<blockquote class="blockquote text-center">
  <p class="mb-0">Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante.</p>
  <footer class="blockquote-footer">Someone famous in <cite title="Source Title">Source Title</cite></footer>
</blockquote>

<blockquote class="blockquote text-right">
  <p class="mb-0">Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante.</p>
  <footer class="blockquote-footer">Someone famous in <cite title="Source Title">Source Title</cite></footer>
</blockquote>

<ul class="list-unstyled">
  <li>Lorem ipsum dolor sit amet</li>
  <li>Consectetur adipiscing elit</li>
  <li>Integer molestie lorem at massa</li>
  <li>Facilisis in pretium nisl aliquet</li>
  <li>Nulla volutpat aliquam velit
    <ul>
      <li>Phasellus iaculis neque</li>
      <li>Purus sodales ultricies</li>
      <li>Vestibulum laoreet porttitor sem</li>
      <li>Ac tristique libero volutpat at</li>
    </ul>
  </li>
  <li>Faucibus porta lacus fringilla vel</li>
  <li>Aenean sit amet erat nunc</li>
  <li>Eget porttitor lorem</li>
</ul>

.list-inline {
  padding-left: 0;
  list-style: none;
}
.list-inline-item {
  display: inline-block;
}
.list-inline-item:not(:last-child) {
  margin-right: 0.5rem;
}

<ul class="list-inline">
  <li class="list-inline-item">Lorem ipsum</li>
  <li class="list-inline-item">Phasellus iaculis</li>
  <li class="list-inline-item">Nulla volutpat</li>
</ul>

<dl class="row">
  <dt class="col-sm-3">Description lists</dt>
  <dd class="col-sm-9">A description list is perfect for defining terms.</dd>

  <dt class="col-sm-3">Euismod</dt>
  <dd class="col-sm-9">
    <p>Vestibulum id ligula porta felis euismod semper eget lacinia odio sem nec elit.</p>
    <p>Donec id elit non mi porta gravida at eget metus.</p>
  </dd>

  <dt class="col-sm-3">Malesuada porta</dt>
  <dd class="col-sm-9">Etiam porta sem malesuada magna mollis euismod.</dd>

  <dt class="col-sm-3 text-truncate">Truncated term is truncated</dt>
  <dd class="col-sm-9">Fusce dapibus, tellus ac cursus commodo, tortor mauris condimentum nibh, ut fermentum massa justo sit amet risus.</dd>

  <dt class="col-sm-3">Nesting</dt>
  <dd class="col-sm-9">
    <dl class="row">
      <dt class="col-sm-4">Nested definition list</dt>
      <dd class="col-sm-8">Aenean posuere, tortor sed cursus feugiat, nunc augue blandit nunc.</dd>
    </dl>
  </dd>
</dl>

html {
  font-size: 1rem;
}

@include media-breakpoint-up(sm) {
  html {
    font-size: 1.2rem;
  }
}

@include media-breakpoint-up(md) {
  html {
    font-size: 1.4rem;
  }
}

@include media-breakpoint-up(lg) {
  html {
    font-size: 1.6rem;
  }
}

.img-fluid {
  max-width: 100%;
  height: auto;
}

<p><img src="../images/img_01.jpg" class="img-fluid" alt="..."></p>

<p><img src="../images/img_02.jpg" class="img-thumbnail" alt="..."></p>

.img-thumbnail {
  padding: 0.25rem;
  background-color: #fff;
  border: 1px solid #dee2e6;
  border-radius: 0.25rem;
  max-width: 100%;
  height: auto;
}

<div class="clearfix">
  <img src="../images/03.jpg" class="float-left" alt="...">
  <img src="../images/03.jpg" class="float-right rounded" alt="...">
</div>

<p><img src="../images/03.jpg" class="mx-auto d-block rounded-circle" alt="..."></p>

.mx-auto {
  margin-right: auto !important;
  margin-left: auto !important;
}

.d-block {
  display: block !important;
}

<div class="text-center">
  <img src="../images/03.jpg" class="img-thumbnail" alt="...">
</div>

<picture>
  <source media="(min-width: 980px)" srcset="../images/img_04_980.jpg">
  <source media="(min-width: 640px)" srcset="../images/img_04_640.jpg">
  <img src="../images/img_04_320.jpg" class="img-fluid img-thumbnail" alt="..."> 
</picture>   

<table class="table">
  <thead>
    <tr>
      <th scope="col">#</th>
      <th scope="col">First</th>
      <th scope="col">Last</th>
      <th scope="col">Handle</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th scope="row">1</th>
      <td>Mark</td>
      <td>Otto</td>
      <td>@mdo</td>
    </tr>
    <tr>
      <th scope="row">2</th>
      <td>Jacob</td>
      <td>Thornton</td>
      <td>@fat</td>
    </tr>
    <tr>
      <th scope="row">3</th>
      <td>Larry</td>
      <td>the Bird</td>
      <td>@twitter</td>
    </tr>
  </tbody>
</table>

<table class="table table-dark">
  <thead>
    <tr>
      <th scope="col">#</th>
      <th scope="col">First</th>
      <th scope="col">Last</th>
      <th scope="col">Handle</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th scope="row">1</th>
      <td>Mark</td>
      <td>Otto</td>
      <td>@mdo</td>
    </tr>
    <tr>
      <th scope="row">2</th>
      <td>Jacob</td>
      <td>Thornton</td>
      <td>@fat</td>
    </tr>
    <tr>
      <th scope="row">3</th>
      <td>Larry</td>
      <td>the Bird</td>
      <td>@twitter</td>
    </tr>
  </tbody>
</table>

<table class="table">
  <thead class="thead-dark">
    <tr>
      <th scope="col">#</th>
      <th scope="col">First</th>
      <th scope="col">Last</th>
      <th scope="col">Handle</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th scope="row">1</th>
      <td>Mark</td>
      <td>Otto</td>
      <td>@mdo</td>
    </tr>
 　　・・・中略・・・
  </tbody>
</table>

<table class="table">
  <thead class="thead-light">
    <tr>
      <th scope="col">#</th>
      <th scope="col">First</th>
      <th scope="col">Last</th>
      <th scope="col">Handle</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th scope="row">1</th>
      <td>Mark</td>
      <td>Otto</td>
      <td>@mdo</td>
    </tr>
 　　・・・中略・・・
  </tbody>
</table>

<table class="table table-striped">
  <tr>
    <th scope="col">#</th>
    <th scope="col">First</th>
    <th scope="col">Last</th>
    <th scope="col">Handle</th>
  </tr>
  <tr>
    <th scope="row">1</th>
    <td>Mark</td>
    <td>Otto</td>
    <td>@mdo</td>
  </tr>
  <tr>
    <th scope="row">2</th>
    <td>Jacob</td>
    <td>Thornton</td>
    <td>@fat</td>
  </tr>
  <tr>
    <th scope="row">3</th>
    <td>Larry</td>
    <td>the Bird</td>
    <td>@twitter</td>
  </tr>
</table>

<table class="table table-striped">
  <thead>
    <tr>
      <th scope="col">#</th>
      <th scope="col">First</th>
      <th scope="col">Last</th>
      <th scope="col">Handle</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th scope="row">1</th>
      <td>Mark</td>
      <td>Otto</td>
      <td>@mdo</td>
    </tr>
    <tr>
      <th scope="row">2</th>
      <td>Jacob</td>
      <td>Thornton</td>
      <td>@fat</td>
    </tr>
    <tr>
      <th scope="row">3</th>
      <td>Larry</td>
      <td>the Bird</td>
      <td>@twitter</td>
    </tr>
  </tbody>
</table>

<table class="table table-striped table-dark">
  <thead>
    <tr>
      <th scope="col">#</th>
      <th scope="col">First</th>
      <th scope="col">Last</th>
      <th scope="col">Handle</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th scope="row">1</th>
      <td>Mark</td>
      <td>Otto</td>
      <td>@mdo</td>
    </tr>
   ・・・中略・・・
  </tbody>
</table>

<table class="table table-bordered">
  <thead>
    <tr>
      <th scope="col">#</th>
      <th scope="col">First</th>
      <th scope="col">Last</th>
      <th scope="col">Handle</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th scope="row">1</th>
      <td>Mark</td>
      <td>Otto</td>
      <td>@mdo</td>
    </tr>
    <tr>
      <th scope="row">2</th>
      <td>Jacob</td>
      <td>Thornton</td>
      <td>@fat</td>
    </tr>
    <tr>
      <th scope="row">3</th>
      <td colspan="2">Larry the Bird</td>
      <td>@twitter</td>
    </tr>
  </tbody>
</table>

<table class="table table-borderless">
  <thead>
    <tr>
      <th scope="col">#</th>
      <th scope="col">First</th>
      <th scope="col">Last</th>
      <th scope="col">Handle</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th scope="row">1</th>
      <td>Mark</td>
      <td>Otto</td>
      <td>@mdo</td>
    </tr>
    <tr>
      <th scope="row">2</th>
      <td>Jacob</td>
      <td>Thornton</td>
      <td>@fat</td>
    </tr>
    <tr>
      <th scope="row">3</th>
      <td colspan="2">Larry the Bird</td>
      <td>@twitter</td>
    </tr>
  </tbody>
</table>

<table class="table table-hover">
  <thead>
    <tr>
      <th scope="col">#</th>
      <th scope="col">First</th>
      <th scope="col">Last</th>
      <th scope="col">Handle</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th scope="row">1</th>
      <td>Mark</td>
      <td>Otto</td>
      <td>@mdo</td>
    </tr>
    <tr>
      <th scope="row">2</th>
      <td>Jacob</td>
      <td>Thornton</td>
      <td>@fat</td>
    </tr>
    <tr>
      <th scope="row">3</th>
      <td colspan="2">Larry the Bird</td>
      <td>@twitter</td>
    </tr>
  </tbody>
</table>

<table class="table table-sm">
  <thead>
    <tr>
      <th scope="col">#</th>
      <th scope="col">First</th>
      <th scope="col">Last</th>
      <th scope="col">Handle</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th scope="row">1</th>
      <td>Mark</td>
      <td>Otto</td>
      <td>@mdo</td>
    </tr>
    <tr>
      <th scope="row">2</th>
      <td>Jacob</td>
      <td>Thornton</td>
      <td>@fat</td>
    </tr>
    <tr>
      <th scope="row">3</th>
      <td colspan="2">Larry the Bird</td>
      <td>@twitter</td>
    </tr>
  </tbody>
</table>

<!-- tr 要素（行）に設定する場合 -->
<tr class="table-active">...</tr>
<tr class="table-primary">...</tr>
<tr class="table-secondary">...</tr>
<tr class="table-success">...</tr>
<tr class="table-danger">...</tr>
<tr class="table-warning">...</tr>
<tr class="table-info">...</tr>
<tr class="table-light">...</tr>
<tr class="table-dark">...</tr>

<table class="table table-bordered">
  <colgroup>
    <col class="table-primary">
  </colgroup>
  <colgroup class="table-success">
    <col>
  </colgroup>
  <colgroup class="table-danger">
    <col>
  </colgroup>
  <tr>
    <th>要素名</th>
    <th>概要</th>
    <th>備考</th>
  </tr>
  <tr>
    <td>col </td>
    <td>同じ列に属するセル（td 要素）を一まとまりの要素として扱う</td>
    <td>空要素。XHTMLの場合は /&gt; で閉じます</td>
  </tr>
  <tr>
    <td>colgroup </td>
    <td>col 要素をグループ化する</td>
    <td>列の構造的なグループ化のために使用</td>
  </tr>
</table>

<!-- td または th 要素（セル）に設定する場合 -->
<tr>
  <td class="table-active">...</td>
  <td class="table-primary">...</td>
  <td class="table-secondary">...</td>
  <td class="table-success">...</td>
  <td class="table-danger">...</td>
  <td class="table-warning">...</td>
  <td class="table-info">...</td>
  <td class="table-light">...</td>
  <td class="table-dark">...</td>
</tr>

<table class="table table-dark">
  <thead>
    <tr>
      <th scope="col">#</th>
      <th scope="col">Heading</th>
      <th scope="col">Heading</th>
    </tr>
  </thead>
  <tbody>
    <tr class="bg-primary">
      <th scope="row">1</th>
      <td>Cell</td>
      <td>Cell</td>
    </tr>
    <tr>
      <th scope="row">2</th>
      <td>Cell</td>
      <td>Cell</td>
    </tr>
    <tr class="bg-success">
      <th scope="row">3</th>
      <td>Cell</td>
      <td>Cell</td>
    </tr>
    <tr>
      <th scope="row">4</th>
      <td>Cell</td>
      <td>Cell</td>
    </tr>
    <tr class="bg-info">
      <th scope="row">5</th>
      <td>Cell</td>
      <td>Cell</td>
    </tr>
    <tr>
      <th scope="row">6</th>
      <td>Cell</td>
      <td>Cell</td>
    </tr>
    <tr class="bg-warning">
      <th scope="row">7</th>
      <td>Cell</td>
      <td>Cell</td>
    </tr>
    <tr>
      <th scope="row">8</th>
      <td>Cell</td>
      <td>Cell</td>
    </tr>
    <tr class="bg-danger">
      <th scope="row">9</th>
      <td>Cell</td>
      <td>Cell</td>
    </tr>
  </tbody>
</table>

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

caption {
  padding-top: 0.75rem;
  padding-bottom: 0.75rem;
  color: #6c757d;
  text-align: left;  /* 左寄せ */
  caption-side: bottom; /* 下に配置 */
}

<table class="table">
  <caption>List of users（キャプション）</caption>
  <thead>
    <tr>
      <th scope="col">#</th>
      <th scope="col">First</th>
      <th scope="col">Last</th>
      <th scope="col">Handle</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th scope="row">1</th>
      <td>Mark</td>
      <td>Otto</td>
      <td>@mdo</td>
    </tr>
    <tr>
      <th scope="row">2</th>
      <td>Jacob</td>
      <td>Thornton</td>
      <td>@fat</td>
    </tr>
    <tr>
      <th scope="row">3</th>
      <td>Larry</td>
      <td>the Bird</td>
      <td>@twitter</td>
    </tr>
  </tbody>
</table>

<div class="table-responsive">
  <table class="table">
    <thead>
      <tr>
        <th scope="col">#</th>
        <th scope="col">Heading</th>
        ・・・中略・・・
        <th scope="col">Heading</th>
      </tr>
    </thead>
    <tbody>
      <tr>
        <th scope="row">1</th>
        <td>Cell</td>
        ・・・中略・・・
      </tr>
    </tbody>
  </table>
</div>

<div class="table-responsive-lg">
  <table class="table">
        ・・・中略・・・
  </table>
</div>