Can't customize padding or line height of syntax element when background-color applied

I’m new to Atom. I’m trying to customize the syntax highlighting by way of a custom theme. I generated the theme with the built-in theme generator, and tweaked from there. I have almost everything working as expected, but I notice that when I apply the background-color CSS to syntax elements, the background colour bleeds outside the height of the lines. I’ve tried to adjust this in the theme, but even when Inspect-Element-ing the lines, there doesn’t appear to be any padding or margin applied, and adjusting line-height doesn’t seem to help.

Screenshot_20190705_222615

Observe how the bleeding is so bad that characters with descenders (“ygpqj” in line 448 of the screenshot) are truncated by the background colour painting.