Fix website CSS and links

[wsxrdv]

There was a broken link to guides. Connected to withastro/starlight#966

[coveralls]

Pull Request Test Coverage Report for Build 10883239437

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 80.4%

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Totals
Change from base Build 10877863362:	0.0%
Covered Lines:	2252
Relevant Lines:	2801

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💛 - Coveralls