There's only a single line in that .css file because the default theme Adwaita comes as a binary:
Adwaita is a complex theme, so to keep it maintainable it's written
and processed in SASS, the generated CSS is then transformed into a
gresource file during gtk build and used at runtime in a non-legible
or editable form.
For gnome 4.* per the README:
How to tweak the theme
Default is a complex theme, so to keep it maintainable it's written
and processed in SASS. The generated CSS is then transformed into a
gresource file during gtk build and used at runtime in a non-legible
or editable form.
It is very likely your change will happen in the _common.scss file.
That's where all the widget selectors are defined. Here's a rundown of
the "supporting" stylesheets, that are unlikely to be the right place
for a drive by stylesheet fix:
_colors.scss - global color definitions. We keep the number of defined
colors to a necessary minimum, most colors are derived
from a handful of basics. It covers both the light variant
and the dark variant.
_colors-public.scss - SCSS colors exported through gtk to allow for 3rd party
apps color mixing.
_drawing.scss - drawing helper mixings/functions to allow easier
definition of widget drawing under specific context. This
is why Default isn't 15000 LOC.
_common.scss - actual definitions of style for each widget. This is
where you are likely to add/remove your changes.
You can read about SASS at http://sass-lang.com/documentation/. Once
you make your changes to the _common.scss file, GTK will rebuild the
CSS files.
Also, check the guidelines present in Default-light.scss and Default-dark.scss:
// General guidelines:
// - very unlikely you want to edit something else than _common.scss
// - keep the number of defined colors to a minimum, use the color blending functions
// if you need a subtle shade; - if you need to inverse a color function
// use the @if directive to match for dark $variant
In the same git directory (Default) you'll find the files
_common.scss, _colors.scss, _colors-public.scss and _drawing.scss
For gnome 3.*:
Since the code has been included in gtk+, you can view the source files HERE. As per their readme:
_colors.scss - global color definitions. We keep the number of defined colors to a necessary minimum, most colors
are derived form a handful of basics. It covers both the light variant and the dark variant.
_colors-public.scss - SCSS colors exported through gtk to allow for 3rd party apps color mixing.
_drawing.scss - drawing helper mixings/functions to allow easier definition of widget drawing under specific context.
This is why Adwaita isn't 15000 LOC.
_common.scss - actual definitions of style for each widget. This is where you are likely to add/remove your changes.
In the same git directory (Adwaita) you can find the _*.scss files mentioned above and the reference schemes:
gtk-contained.css
gtk-contained-dark.css
