Black icons in sidebar of gtk file dialogs when using Xfce 4.18 on Ubuntu 22.04 LTS

[juozaspo]

Description

When using Xfce 4.18 black icons are shown in file dialogs after installing latest version of Greybird theme, while on Thunar file manager they appear correctly. The default theme appearance w/o updated theme installed locally has icons appearing correctly. Using Ubuntu 22.04 LTS with xubuntu-dev staging ppa (ppa:xubuntu-dev/staging, https://launchpad.net/~xubuntu-dev/+archive/ubuntu/staging) enabled.

To reproduce

1. (optionally) Create a new test user, login into environment running Xfce 4.18
2. Build and install theme as described in README.md and toggle themes so changes would be applied and then try to use open and/or save dialog.
3. Undo costomizations by moving theme folders away or edit theme as described below, toggle themes once again, observe how icons appear correct again.

Temporary workaround

Undo changes related to sidebar added to gtk-3.0/gtk.css & gtk-3.0/gtk-dark.css by re-adding -gtk-icon-style: regular; to style rule next to comment /*********** Sidebar * */, e.g. change .sidebar { border-style: none; background-color: #dae0e6; } to .sidebar { border-style: none; background-color: #dae0e6; -gtk-icon-style: regular; } in gtk-3.0/gtk.css of the Greybird theme.

Screenshots

Before: sidebar icons appear correctly

After: sidebar icons appear broken

For reference: This is default appearance of sidebar icons on Thunar, notice they appear correctly

Commit: ffa9846
Commit causing the bug: 173428b
System-wide greybird theme is from ppa, most of xfce packages also from the same ppa.