fix(skip-to-content): make link text white to meet AA contrast

[jendowns]

Closes #570

Changelog

Changed

• make the SkipToContent link text white so that it makes AA minimum contrast requirements

[vercel]

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(da029af, update in progress)

[vpicone]

Ah that's annoying, it's comparing using the link blue rather than the white it uses when it's actually rendered. So I don't think it's an actual violation, but good to get clear out the DAP error either way.