Adrián Pérez de Castro authored Apr 26, 2018 and Michael Catanzaro committed Apr 30, 2018

In particular, the theming for the incognito windows tends to look odd
with themes other than Adwaita. It is possible to load different CSS
resources depending on the selected theme by handling changes to the
GtkSettings::gtk-theme-name property: this splits the CSS into a
"shared.css" part which contains the rules which play well with most
themes, and an "Adwaita.css" which builds upon the shared CSS rules
and is loaded only for the Adwaita theme. The CSS code is still
generated from SCSS, with definitions used by SCSS snippets moved
into a new _definitions.scss file to avoid repeating them.

Note that instead of manually handling theme changes, EphyEmbedShell
is changed to inherit from DzlApplication (instead of GtkApplication),
which already implements the desired CSS resource loading behaviour.
This makes the existing CSS loading code unneeded, and therefore it
is removed. Also, the resources are moved into the resource path
/org/gnome/Epiphany/themes as expected by DzlApplication.

https://bugzilla.gnome.org/show_bug.cgi?id=783912