The code block CSS had a vertical strip of white just to the left of the

actual code being displayed. This was due to a :before rule that

didn't have a background set, getting the background instead from the

parent container.
This change adds a background: inherit to ensure it gets the

background color set by the element it's part of.

Tested that this looked correct on Firefox and Chrome.
Checked code blocks in text fields (like Description), which dock to edges,

and in reviews.