Why are h5 and h6 left unstyled? - JayPanoz/Soma GitHub Wiki

If you feel the urge to reach for a heading of level 4 or greater, consider redesigning your document (Tufte CSS)

I’m cool with the idea h4 may be useful for very complex outlines (like in programming books) but that’s my personal limit. This is the reason why those two headings are left unstyled.