[color]: dark-mode sidebar nav link have bad contrast ratio

[pranshuchittora]

🐛 Bug Report

(A clear and concise description of what the bug is)
The sidebar nav links in the dark mode have bad contrast ratio.

Have you read the Contributing Guidelines on issues?

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To Reproduce

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1. Visit https://create-react-app.dev/docs/deployment/#docsNav and toggle dark mode

Expected behavior

Refer accessibility docs to background and foreground colour contrast ratio

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Actual Behavior

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Reproducible Demo

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