CSS - change UI action button background colour

[gmcr.cz (GM group & Co, s.r.o.)]

I have a UI action wokflow button placed on PanelHeader.

I want the first button to have a limy background colour like so

Is there a way to place CSS code in some CSS file taht is loaded with the page?

#7deb9e38-9e4e-40fc-b855-138fb7151796 {
background-color: lime;
}

[gmcr.cz (GM group & Co, s.r.o.)]

Well accorcing to Syntax and basic data types IDs should not start with number, which is this case.

If I change the guid in model into one not starting with number it works.

[jsusen (Jindřich Sušeň)]

This is not officially supported. You can fork origam and add the feature or you can hack it. There is a minified css file in the dist directory. You could edit it but the file will be overwritten every time you updrade… Not a great solution.
This is what I managed to do in the demo project:

[gmcr.cz (GM group & Co, s.r.o.)]

Thank you for your reply.

So far I stick with this solution. I finally placed custom.css in customAsset folder and I do reference it in the minified css file as you mentioned.