Update index.css

[vikashmurugesh]

Add dark/bright mode toggle button
solved issue

Description

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Related Issues*

• Fixes #(issue number)

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After changes:
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Checklist

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• I have forked the repo and pushed the changes according to contribution guidelines.
• I have tested these changes locally.
• I have tried to maintain the consistency of the code.
• I have tested these changes locally.
• I have updated the documentation accordingly.

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[github-actions]

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