The markdown step files contain quite some HTML: at the moment, for example,
header and navigation buttons are all written explicitly in the markdown files
as raw HTML (also the <details> blocks are possible because of this).
Nothing prevents you from further mixing markdown and custom HTML, for example if you want to alter the appearance of the navigation.
Clicking on this paragraph is a weird way to go back to previous step.
Just keep in mind that the Katapod engine will not inspect the HTML (for example, you won't have properly-styled tables or embedded from-repo images out-of-the-box).
You can even plan a nonlinear step sequence for your scenario, and design navigation accordingly. Here we pretend the following step can be done in two ways: