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+Summary
+-------
+
+* To be able to use the latest/adequate version of sass, install sassc
+* meson will regenerate the CSS every time you modify the SCSS files.
+* Note that meson always builds out-of-tree, so the modified css files will
+  appear in your builddir.
+
+Theme variants
+--------------
+
+The Default theme comes in 4 variants: light, dark, hc (highcontrast) and
+hc-dark (highcontrast inverse). The generated CSS files for the variants
+are called Default-$variant.css. For technical reasons, GTK adds one level
+of include wrappers around these, which are called gtk-$variant.css.
+
+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.