preferences-page: Support CSS

Fixes GNOME/libhandy#380
11 jobs for css-support in 12 minutes and 59 seconds (queued for 1 second)
latest
Status Name Job ID Coverage
  Build
passed api-visibility #1051452

00:00:28

passed build-debian-clang #1051454

00:02:59

passed build-debian-gcc #1051453

00:02:11

passed build-fedora-gcc #1051455

00:04:51

passed build-flatpak #1051456
flatpak

00:01:20

passed build-flatpak-glade #1051457
flatpak

00:03:08

 
  Test+Docs
passed build-gtkdoc #1051458

00:02:35

passed unit-test #1051459

00:02:35

46.0%
 
  Package
passed package-debian-buster #1051460

00:02:14

 
  Test Package
passed autopkgtest-debian-buster-package #1051461

00:03:16

passed lintian-debian-buster-package #1051462

00:01:05