Option to inject custom css/styles

[jonostanck]

Hey,

It would be great if you guys could add (eg. in User Interface settings section) some kind of textarea where we can place custom css/styles to override MASS default ones. This way we would be able to hide specific dom elements or change the default font for headings making it blend even more with lovelace.

Thanks for this amazing addon that allowed me to finally connect all my speakers into one huge playing instance!