Doesn't work with adwaita / radiance

[jakejarrett]

System default themes don't appear to be file based, need to work out a way to support this

[jakejarrett]

Notes:

• Yaru includes its gtk.gresource file locally in /usr/share/themes/Yaru/gtk-3.0

Once we find the gresource file, we need to run the following commands to extract the assets (incl css)

# Confirm css is present
gresource list /path/to/filename.gresource | grep ".css"

# If Present
gresource extract /path/to/filename.gresource /path/to/resource

# Provide the css file to consumer
/path/to/resource/gtk.css