PF6 custom style followup

[wise-king-sullyman]

Followup to #3966, which commented out some custom styles which were removed in core as a temporary measure to unblock other work.

Noted styling issues:

• Cookie banner/message needs to have a background.
• The blue links in the black section at the bottom of the page aren't accessible. Are we keeping the black background I wonder?
• Get started->Community page - the vertical spacing of sections, headers, etc, is missing
• I don't see code snippet highlights on react component pages
• Code snippet highlights run into each other (HTML page) Do we want a little more space or no?
• Training pages, the cards are messed up https://patternfly-org-pr-3996-site.surge.sh/training/html It looks like instead of a label, we have a tiny card?
• Utilities - Dark theme dotted outlines on some examples are too light, e.g. https://patternfly-org-pr-3996-site.surge.sh/utility-classes/flex They seem to be good on the layouts.
• Contrast checker uses hardcoded values