Improve CardSubheading text contrast

[jonnyelliot]

The CardSubheading text is a bit hard to read.

The contrast ratio is below the recommended 4.5

Looks like it is the $textSecondary color against a white background ($paper).

[jonnyelliot]

Same for the dark theme

[jonnyelliot]

Chrome's recommendation is #767572 for the light theme text and #8b8a86 for the dark.

[stuarthendren]

That dark screenshot looks wrong, the text should not be black. Might be a bigger/different issue.

I don't think we need AAA for the subheading, but should probably aim for AA.

[github-actions]

🎉 This issue has been resolved in version 5.1.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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