Improve web accessibility for theme base16 comments

[designbymimmi]

Context

Increase color vs background color contrast in base16 theme to make it easier to read comments.

Screenshots using theme base16.dark

Before #505050	After #858585

Web accessibility test results

Before	After

Considerations

Tried to keep the comment color as "dark" as possible to keep it inline with the style of the theme while still improving the accessibility.

[epidemian]

This is really nice. I personally find most dark themes unusable due to comments being so dark they are almost unreadable.

Luckily it's usually a simple config change to increase the contrast of comments. But dang, we shouldn't have these defaults :/