Improve font size of headings in the generated site

[kinow]

Not sure if this issue needs to be reported here or in the website repository.

The font size of headings like h5 is too small IMO.

Below we have CommandInputRecordField and its fields, but it's visually confusing to distinguish what's the topic and what's a section or part of the topic.

[tetron]

The doc generation is a schema salad feature, so maybe put in an issue there and link it here.

It's just a styling thing, we want to override the default bootstrap styling that is making the heading too small.