Changing R Code font in .rpres RMarkdown via CSS

Question

I'm trying to back into how to hand craft a CSS file to override some settings in my *.rpres in order to change the font in the resulting HTML. I can change some bits, but I can't grok how to change the R Code blocks.

Using the inspector on in Chrome, I see the following:

So after significant futzing around it seems like I should be able to override this with the following CSS entry:

.reveal code .r {
  font-size: 180%;
  font-weight: bold;
   color: green;
}

Only that doesn't seem to change a thing.

Any tips on how I can change the font for <code class="r"> with my CSS file?