[Feature]: Theme support

[kbuczynski-nashpl]

Describe the feature

As a user i would like to chose black as a background colour and opacity to match elv ui addon

Describe the implementation

As a user i would like to chose a background colour and its opacity in options.

[Cidan]

Editing the title, using this bug to track the addition of theme support.

[rodalpho]

Definitely looking for this feature before I switch. I want the background pure black.

[JasonDepp]

in list view I see blocks... expecting to have the ability to change my font, maybe can fix that... ps: a player from zhCN game version WLK3.4.3