[FEATURE REQUEST] Add an "appearance" section in settings

### Please confirm these before moving forward

- [X] I have searched for my feature proposal and have not found a work-in-progress/duplicate/resolved/discarded issue.
- [X] This proposal is a completely new feature. If you want to suggest an improvement or an enhancement, please use [this template](https://github.com/marticliment/WingetUI/issues/new?assignees=marticliment&labels=enhancement&projects=&template=enhancement-improvement.yml&title=%5BENHANCEMENT%5D+%28Enter+your+description+here%29)

### Describe the new feature

**Add an "appearance" section in settings.**
# Where?
The section would be best under the"General" section of the settings menu.

### Describe how this new feature could help users.

# Why?
This can let users have a more customized package manager and feel at home.
# What?
This feature can let users customize
- transparency
- acrylic look
- apply specific colors
- icons
- and even **CSS!**
# Why **CSS**?
Kind of like how Firefox has a [css store with many custom themes,](https://firefoxcss-store.github.io/)
Why not give that feature to WingetUI?
***In my opinion, i think having UI in an app name means you can customize it to however you like.***