[Feature]: Additional colours for theme.css

[bubblobill]

Describe the Problem

There are colours defined in themes that are not available to users in available CSS.
Current theme CSS aims at matching UI elements with common HTML elements into a simple usable construction.
This leaves out many settings that have not been implemented into the CSS yet and renders them inaccessible when using things like handlebars to construct stat-sheets.

The Solution you'd like

Extend the custom CSS properties defined in the root element to reflect properties defined in theme property files.
This eill allow users to extract particular values for known names
e.g. from

Panel.background = @baseColour
ProgressBar.arc = 6
ProgressBar.background = @col20
ProgressBar.foreground = @blue
ScrollBar.background = @col20
ScrollBar.showButtons = true
ScrollBar.thumb  = @col50

to

--panel-background : blah;
--progress-bar-arc : blah;
--progress-bar-background : blah;
--progress-bar-foreground : blah;
--scroll-bar-background : blah;
--scroll-bar-showbuttons : blah;
--scroll-bar-thumb  : blah;

Alternatives that you've considered.

No response

Additional Context

No response