Warty Brown theme causes GTK3 Snap apps to use Adwaita theme

Expected Behavior

Snap apps should use Yaru Warty Brown theme, with Yaru menus and brown colours

Actual Behavior

Snap apps use Adwaita theme, with blue colours and semi-gradiented title bar. Also blue background in menu highlights.

This issue only happens with Warty Brown theme, other versions of the Yaru theme are not affected.

Steps to Reproduce the Problem

Get Oracular daily build and update it
Open GNOME Control Centre, go to "Appearance", click Warty Brown
Open any Snap GTK3 app (like Firefox and Thunderbird)
For Firefox, look at the address bar and right click in the page - you will see blue coloured menu items
For Thunderbird, open About page and notice blue links, also the tab top border is blue

Software that presents the issue

$ snap list
...
firefox                    130.0-2          4848   latest/stable/…  mozilla✓    -
...
gtk-common-themes          0.1-81-g442e511  1535   latest/stable    canonical✓  -
...
thunderbird                128.2.0esr-1     509    latest/stable/…  canonical✓  -

Yaru version

$ apt policy yaru-theme-gtk
yaru-theme-gtk:
  Installed: 24.10.4-0ubuntu1
  Candidate: 24.10.4-0ubuntu1
  Version table:
 *** 24.10.4-0ubuntu1 500
        500 http://archive.ubuntu.com/ubuntu oracular/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu oracular/main i386 Packages
        100 /var/lib/dpkg/status

Ubuntu version

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu Oracular Oriole (development branch)
Release:    24.10
Codename:   oracular

$ cat /var/log/installer/media-info 
Ubuntu 24.10 "Oracular Oriole" - Daily amd64 (20240822)

Screencast Attached is a screencast, which shows behaviour for both Yaru (orange) and Yaru Warty Brown themes.

Screencast From 2024-09-11 14-13-55.webm

ubuntu / yaru

Warty Brown theme causes GTK3 Snap apps to use Adwaita theme #4139