Add Dark Theme For Users

[dilaann]

Most apps have dark and light themes by default.

I usually prefer a dark theme if there is an option. I thought it might be a good idea to offer this option to users for GOAT and the new project. It's not urgent but it might be a nice feature to customize.(or maybe user can pick their own colors and own theme,it can be also a good feauture to implement for future UI design )