How to fix this horizontal scroll bar issue?

On my main Mac machine (firefox/safari and chrome) my code tags “box” renders like this:

But, on my Windows (with different screen res) it shows this empty horizontal scroll bar:

I want the scroll bar to only show up when needed, like on my Mac. I have no idea how to fix this. Btw, i’m using this theme (direct link to it’s .css), with a few minor edits, here’s my file.

This is clearly not a Hugo issue, so you’d probably be best to ask this question at Stackoverflow.