If you're looking to implement responsive typography, the Bootstrap 4 documentation has a dedicated section on it. According to the docs: Bootstrap doesn't provide this feature out of the box, but incorporating it is quite straightforward.
The process is actually quite simple. Essentially, you just need to specify the font sizes for different media breakpoints on the <html>
tag.
Here's an illustration:
html { font-size: 1rem; }
@media (min-width: 576px) {
html { font-size: 1.25rem; }
}
@media (min-width: 768px) {
html { font-size: 1.5rem; }
}
@media (min-width: 992px) {
html { font-size: 1.75rem; }
}
@media (min-width: 1200px) {
html { font-size: 2rem; }
}
<div class="container">
<div class="row">
<div class="col-md-12">
<h1>Hello World</h1>
</div>
</div>
</div>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet"/>