Refactor CSS in src/index.tsx

[palisadoes]

Refactor CSS in this file

To improve the UI/UX of Talawa-Admin we have been working on:

1. making the application more suitable to color blind users
2. streamlining all CSS into a single global file

This file contains embedded CSS references that should be completely moved to:

• src/style/app.module.css

Additional information:

1. The foundational work for this was completed in this PR:
   • Chore/css changes #2466
2. The desired single CSS file is:
   • src/style/app.module.css

The challenge:

The goal is for this file to use this new design pattern. This means that:

1. All embedded CSS in this file must be merged into the global CSS file using pre-existing CSS.
2. All embedded CSS in this file must be removed

[devender18]

Hey, could you please assign this to me? :)