Winbox Dark Mode

[sean9101]

According to the below readme. Winbox running in a Wine instance can have a dark mode applied.

https://gist.github.com/Zeinok/ceaf6ff204792dde0ae31e0199d89398

Please could you look into adding this. I am not strong myself in Snap but if you could point me in a direction of how to implement this in the wine prefix that snap creates then I could do it myself if not deemed important enough to add to this project