The code underlying this page is a copy of the Bootstrap "getting started" example using CDN links. See the example.
There is one important addition: I have added a DIV element with the Bootstrap container class applied to it. This DIV contains everything visible on the page. In the same DIV, I also included the mt-5 class to add some space at the top of the container. Without that, the heading is too close to the top of the browser window, and it looks stupid. See the Bootstrap margin classes here.
<div class="container mt-5">
Resize your browser window to see how the container behaves at different widths. For a more obvious example of how the container DIV adapts, using background color, see version 2 of this page.
This page does not include any Bootstrap rows or columns.