Description:
When LibreOffice is run on Linux Mint Cinnamon with a dark GTK theme (e.g. Skeuos-Violet-Dark / Mint-Y Dark Purple / Adwaita:dark), the font selection dropdown (toolbar combobox and also the font list in dialogs) opens with a light/white background and very light gray text for non-hovered entries. Hovering an entry shows the system highlight (violet) and white hovered text, but unhovered entries remain effectively unreadable.

This occurs both with the Flatpak build (org.libreoffice.LibreOffice from Flathub) and with a manually installed DEB build (LibreOffice 25.8.0.4 installed into /opt/libreoffice25.8). I have tried theme overrides, passing GTK_THEME, trying different VCL backends, installing system theme modules, and resetting user profile — the problem persists. The behaviour appears to be a GTK/VCL rendering issue with the combo-box / popover that displays font names, not a simple theme mismatch.

Steps to Reproduce:
1.Use Linux Mint (Cinnamon) with a dark GTK theme (e.g. Skeuos-Violet-Dark or Mint-Y Dark Purple) set system-wide.
2. Install LibreOffice 25.8.0.4 either as Flatpak (Flathub org.libreoffice.LibreOffice) or via manual DEB /opt/libreoffice25.8 build.
3. For Flatpak: flatpak install flathub org.libreoffice.LibreOffice
4. Ensure the app is run with a dark GTK theme (system theme set to dark, or start it with GTK_THEME=Mint-Y-Dark libreoffice / flatpak run --env=GTK_THEME=Mint-Y-Dark org.libreoffice.LibreOffice).
5. Open Writer (or any module) and click the font family dropdown on the toolbar (or open Format → Character → Font tab and open the font list).
6. Observe the dropdown/popover background and text color of the font names.

Actual Results:
The font dropdown opens with a white (or very light) background. Non-hovered font names are rendered in very light gray on white and are nearly unreadable. Hovering an entry applies the system highlight color and shows white text for the hovered entry, but the default/unhovered rendering remains unusable.

Expected Results:
The font dropdown should respect the dark theme: dark background, light/white text for font names, and the same theme behaviour as other widgets. The control should be readable without hover.


Reproducible: Always


User Profile Reset: Yes

Additional Info:
Environment / versions / additional technical details

OS: Linux Mint 21.3 Cinnamon (user reported)

LibreOffice: 25.8.0.4 (manually installed DEB under /opt/libreoffice25.8) and also tested with Flatpak org.libreoffice.LibreOffice — problem present in both.

GTK: app is using GTK3 backend (VCL=gtk3) by default on this system; also tested with other VCL backends.

Themes tested: Skeuos-Violet-Dark, Mint-Y Dark Purple, Adwaita:dark (via GTK_THEME overrides).

Flatpak overrides (examples set during troubleshooting):
filesystem=host, filesystem=host-os, filesystem=host-etc, filesystem=home
/usr/lib/x86_64-linux-gnu/gtk-3.0/modules passed into Flatpak
/usr/share/themes, ~/.themes and /home/user/.themes exposed
xdg-config/fontconfig:ro, xdg-config/gtk-3.0 passed through

Environment variables seen when running Flatpak via Flatseal:
GTK_THEME=Adwaita:dark (was set by Flatpak at one time)
LIBO_FLATPAK=1, JAVA_HOME=/app/jre, GIO_EXTRA_MODULES=/app/lib/gio/modules

Messages observed when attempting GTK backend / Flatpak runs:
Running SAL_USE_VCLPLUGIN=gtk3 flatpak run org.libreoffice.LibreOffice printed:
Gtk-Message: Failed to load module "xapp-gtk3-module"
(This was due to Flatpak sandbox / xapp module not being available; xapps-common exists on system but inside Flatpak it was not visible in some tests.)

Attempts / workarounds already tried:

Using GTK_THEME=... env overrides and Flatpak overrides for GTK_THEME (did not fix).

Attempted to make system xapp GTK module visible to Flatpak; installed xapps-common on host and tried flatpak override --filesystem=/usr/lib/.../gtk-3.0/modules (no success in resolving the combobox rendering).

Tried different VCL plugins: SAL_USE_VCLPLUGIN=gtk3, SAL_USE_VCLPLUGIN=gen, SAL_USE_VCLPLUGIN=kf5 (kf5 produces a different UI but pulls many KDE libs and is not a practical solution for Cinnamon).

Removed Flatpak and manual DEB installs (clean installs) — problem persisted with DEB 25.8.0.4.

Considered / performed profile reset (rename ~/.config/libreoffice to a backup) as part of testing — this did not resolve the font dropdown rendering.

Logs / relevant console outputs (paste these into the bug if asked for logs):

SAL_USE_VCLPLUGIN=gtk3 flatpak run org.libreoffice.LibreOffice →
Gtk-Message: Failed to load module "xapp-gtk3-module"

Flatseal environment snippet:

GTK_THEME=Adwaita:dark
LIBO_FLATPAK=1
GIO_EXTRA_MODULES=/app/lib/gio/modules

dpkg/installation traces (if needed) — I can attach full dpkg -l | grep libreoffice output if required.