The HTML spec defines 6 levels of Headings (h1-h6). Each creates a layer in the document's hierarchy, starting with h1 at the root.

Every page should have an h1 and should use the other levels as needed (starting with h2).

If you don't want a page to have a Heading, use an invisible h1 so screen reader users can still understand the page's hierarchy. To do this, add the class visually-hidden to the h1.

For all other Headings, add the classes heading and level-n (where n is a number 1-6) to set the visual appearance of the Heading. These numbers correspond to the elements h1-h6 in the HTML spec, but the classes and tag names don't have to align; this allows you to visually skip levels while still keeping the document hierarchy consistent.