Badges scale to match the size of the immediate parent element by
using relative font sizing and em units.
<h1>Example heading <span class="badge badge-secondary">New</span></h1>
<h2>Example heading <span class="badge badge-secondary">New</span></h2>
<h3>Example heading <span class="badge badge-secondary">New</span></h3>
<h4>Example heading <span class="badge badge-secondary">New</span></h4>
<h5>Example heading <span class="badge badge-secondary">New</span></h5>
<h6>Example heading <span class="badge badge-secondary">New</span></h6>
<button type="button" class="btn btn-primary">
Profile <span class="badge badge-light">9</span>
<span class="sr-only">unread messages</span>
</button>