H1 font size doesn't respond to custom css

Hi, I’m working on the RTFM skeleton, I managed to change h2, h3, etc font sizes via a custom css file, but for some reason only h1 does not respond to this css. Can anyone give me some pointers on what to do to be able to change the h1 font size as well?

Using Chrome’s DevTools (right-click the element, select inspect) or Firefox’s Firebug (extensions, also right-click), look at the stack trace for the element’s style properties. It will clearly delineate what takes precedence and overrides other styles affecting it.

Thank you so much!