Improve Syntax Highlighting

[erikaheidi]

The current syntax highlighting theme doesn't have a good contrast on dark mode. Ideally, let's use the theme toggle button to also change the syntax highlighting theme when users change from light to dark mode.

[ltagliaferri]

@erikaheidi — I know you made some improvements here, are you satisfied with where we have landed?

[erikaheidi]

I just had a look now, in dark mode I think it still could be better. A different syntax highlighting theme may be able to fix it.

[ltagliaferri]

Let's add this to the reqs / specs for the Hugo dev

[ltagliaferri]

Improvements made with V2 launch