The most precise method I know of is to add the style to your user style sheet (command
Open Your Stylesheet).
Then add this:
but change the font weight value to one that matches the weights typeface has available. In general,
400 is regular and what Atom will tend to use, while
700 is bold (probably too bold for general use unless you really need the contrast). Some fonts like
Source Code Pro (example) have lots of weights, so you could specify
500 and get a slightly heavier weight.
If you aren’t getting the results you want, try a typeface that supports more
Source Code Pro is a great place to start, in my opinion.