Add theme support

[asolochek]

I see this was requested a few years ago and got 0 traction, but I'm hoping it gets more interest now.

Of the cards I use, only the media control card and the entities cards support setting the theme. I'm not sure where that card lives in the HA source, so I can't see how it's implemented there, but I'm going to keep looking. If it looks relatively straight forward, I may take a stab at implementing it. Of course if anyone has some insight about this, that would be useful, too.

[ildar170975]

Currently you can use card-mod to set any css vars for mini-graph-card.

[asolochek]

I just tried that, but as soon as I enable card-mod my dashboard crashes a second after loading. It may be an issue with 2025.1.0

[ildar170975]

Currently we set a minimal priority for things which can be achieved by card-mod.
(at least while card-mod works)
If you have issues with card-mod - suggest to check in Community main card-mod thread first, only then create an issue in card-mod github repo.
(so far we have only 1 confirmed card-mod issue with 2025.1, it is related to entity-rows only)