New tile card percentage not readable in cover position feature

[JohnnyM84]

Hello, I want to use the new tile card in home assistant, but if i use the feature cover position and i use the slider then i get a white box with white text in it so the persentage is not readable. Does somebody know what to add to the theme to solve this problem?

[genehand]

Fix pending in https://github.com/seangreen2/slate_theme/pull/24 :)