Docs accessibility fixes

[joshfarrant]

Summary

List of notable changes:

• Updated Section example to use a background colour with sufficient contrast
• Improved styling of torchlight Card example in docs on very small (320px) viewports

What should reviewers focus on?

• Just check you're happy with the changes

Steps to test:

• Take a look at relevant sections in the Section docs, and the Card docs.

Supporting resources (related issues, external links, etc):

• Towards https://github.com/github/accessibility-audits/issues/10394
• Towards https://github.com/github/accessibility-audits/issues/10368

Contributor checklist:

• All new and existing CI checks pass
• Tests prove that the feature works and covers both happy and unhappy paths
• Any drop in coverage, breaking changes or regressions have been documented above
• UI Changes contain new visual snapshots (generated by adding update snapshots label to the PR)
• All developer debugging and non-functional logging has been removed
• Related issues have been referenced in the PR description

Reviewer checklist:

• Check that pull request and proposed changes adhere to our contribution guidelines and code of conduct
• Check that tests prove the feature works and covers both happy and unhappy paths
• Check that there aren't other open Pull Requests for the same update/change

Screenshots:

Please try to provide before and after screenshots or videos

Before	After

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Latest commit: 100f1e1

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[github-actions]

🟢 No design token changes found

[github-actions]

🟢 No visual differences found

Our visual comparison tests did not find any differences in the UI.