does not work with GTK CSS

[alex-tee]

GTK has this CSS syntax to allow you to define colors:

@define-color bg_dark_variant1 #242c31;

this plugin works in other cases (it highlights the color) but it ignores this. can we please mark these colors as well?

note that it is also ignored wherever this color is used:

entry:focus {
  border-color: @bright_orange;
}

^ this is probably harder to support but @define-color should be simple to implement I think