More issues with dark mode

[gsmet]

The documentation search page is not very readable: https://quarkus.io/guides/#q=infinispan

Two problems in my opinion:

• The grey font is rather dark and for me the contrast is not enough, especially the one for the details
• The link-color is somehow overridden by the .qs-guide CSS to a color that is far too dark

As for the first item, I wonder if it's an issue in the .dark variables and that the highlight color should be lighter.

For the second item, I think it's an issue with the .qs-guide CSS as it shouldn't override the link color.

/cc @marko-bekhta @insectengine

[gsmet]

@marko-bekhta fixed the issue.