Refactor styles to follow MUI

# Refactor

`something.module.scss` don't follow the styling practices outlined in MUI documentation, usage of themes are a lot harder from there. Instead, we should refactor our styling approach as outlined in [MUI customization guide](https://mui.com/material-ui/customization/how-to-customize/)

## Tasks

- [ ] Replace `something.module.scss` files with style objects importable by MUI objects
- [ ] Extend/validate styling/UI guidelines to explain best approaches and provide links to useful documentation @VakarisZ