Improve contrast of highlighted line during debug

[kartzke]

Hi, love this theme! My only challenge with it is during debug. The line that gets highlighted is bright yellow, and it's nearly impossible to see the code on that line. Screenshot attached.

Is it possible to change the color of the line highlight to improve legibility?

[kartzke]

I think this fixes it, but I've never worked with theming before, so lmk if more changes are needed:

#10