Low contrast on some highlights

See screenshot attached from the test on xwiki.org, the highlighter does not have default colors that comply with WCAG standards.

There doesn't seem to be one highlighting theme that's accessible yet (https://github.com/PrismJS/website/issues/29), but they did identify the main painpoints https://github.com/PrismJS/prism/pull/2313 . Note that by default our code boxes have a grey background, we might need to make it white or have our own color changes to respect a minimum contrast of 4.5 .

Note that this accessibility issue should be solved if we ever want to move this as the default implementation of the code macro in XS