Theme improvements (#822)

* start converting

* small fixes

* reorganize theme files

* cleanup search bar

* increase spacing

* small tweaks

* fix select styles in Chrome

* cleanup menus

* improve button icons

* restore badges

* remove unused classes

* restore some overrides

* restore bookmark form

* add summary outline

* avoid layout shifts

* restore bookmark details

* increase border radius for modals

* improve details modal

* restore reader mode

* restore settings

* cleanup variables

* start with dark theme

* more dark theme...

* more light theme...

* more dark theme...

* add postcss build

* remove sass processor

* update docker build

* fix alt color

* remove endless symbol

* fix tests

* update assets

* remove sass files

* fix docker build

* cleanup spacing

* improve theme

* update test scripts

* update CI workflow

* fix test

requirements.txt

@@ -35,8 +35,6 @@ django==5.0.8
     #   mozilla-django-oidc
 django-registration==3.4
     # via -r requirements.in
-django-sass-processor==1.4
-    # via -r requirements.in
 django-widget-tweaks==1.5.0
     # via -r requirements.in
 djangorestframework==3.15.2