Adjust font size of issue titles and h2s

Our issue templates use ## or h2 for sections, but when rendered, the font size of the section headers is about the same size as the issue titles. (Inspected just now and it says 24px vs 23px.) I'd think an h2 would be much smaller than a title. Did this change recently? Can we reduce the size of h2s inside an issue? Or do we really need to standardize of ###? It seems wrong to semantically change our markdown usage just to make things look reasonable.