fine-grained CSS variables

[akosyakov]

We use CSS variables for theming. Right now most of the variables are generic and changing them can break some parts of UI. It would be nice to introduce semantic specific CSS variables to have more fine-grained control.

[svenefftinge]

I don't think they should be extension specific, but they should be semantic. I.e. naming common UI elements, like we started doing with the scrollbar, buttons and dialogs already.

[spoenemann]

@akosyakov how is this related to #1504? Do you propose to replace the existing variables using new names, or to add new variables in addition to the existing ones?

[akosyakov]

No, it is not related, it is about adding new variables.

[spoenemann]

Could be of help here:
https://code.visualstudio.com/docs/getstarted/theme-color-reference