Create heading without changing font or style

I am working on a couple of sites and know that headings are important for search engine optimization, however, whenever I try to create a heading to improve our SEO rating, the font style changes dramatically. I am not by any means experienced with code but I understand that the font style for the headings is part of the themes CSS. Is there a way to apply a heading style (h1 or h2 for example) in the theme, but have the font keep its current style? I really appreciate any help in this regard! Thank you!