Bootstrap 5 Default Settings

Bootstrap 5 uses a default font-size of 1rem (16px by default), and its line-height is 1.5.

In addition, all <p> elements have margin-top: 0 and margin-bottom: 1rem (16px by default).

<h1> - <h6>

Bootstrap 5 styles HTML headings (<h1> to <h6>)  with a bolder font-weight and a responsive font-size.

Display Headings

Display headings are used to stand out more than normal headings (larger font-size and lighter font-weight), and there are six classes to choose from: .display-1 to .display-6:

<Small></small> Element

In Bootstrap 5 the HTML <small> element (and the .small class) is used to create a smaller, secondary text in any heading:

<div class="container mt-3">
  <h1>Smaller, Secondary Text</h1>
  <p>The small element (and the .small class) is used to create a smaller, secondary text in any heading:</p>       
  <h1 class="small">h1 heading <small>secondary text</small></h1>
  <h2>h2 heading <small>secondary text</small></h2>
  <h3>h3 heading <small>secondary text</small></h3>
  <h4>h4 heading <small>secondary text</small></h4>
  <h5>h5 heading <small>secondary text</small></h5>
  <h6 class="small">h6 heading <small>secondary text</small></h6>
</div>

<mark>

Bootstrap 5 will style <mark> and .mark with a yellow background color and some padding: