Make the dark mode functional in login page of issue #91

[abansal15]

Overview

1. This PR fixes or fixes part of [BUG]: Dark mode not working in login page #91 .
2. This PR does the following: [This pr makes the dark mode functional in log in page]

Essential Checklist

• The PR title starts with "Fix [BUG]: Dark mode not working in login page #91 : ", followed by a short, clear summary of the changes. (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• "Allow edits from maintainers" is checked. (See here for instructions on how to enable it.)
• The PR is made from a branch that's not called "main/master".

Proof that changes are correct

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