Flatpak GTK Applications Display Improperly

77Z · 2025-05-13 23:18:13

I'm having trouble getting Flatpak GTK4 applications to display correctly on my system. As shown in the screenshot below, there is a clear mismatch between the two themes, and I'd like the Flatpak version to appear properly as it does on the right.

Theme mismatch between the Flatpak and native versions of an example GTK4 app, Blanket
Theme mismatch between the Flatpak and native versions of an example GTK4 app, Blanket.

I'm assuming this is most likely an issue with my Arch system and not Flatpaks in general, as Flathub screenshots display properly themed GTK4 applications that upon installing on my system, look nothing like these screenshots. I'd also like to note that I am currently using KDE Plasma as my desktop environment, but these issues seem to persist across DE's. I tested on GNOME as well.

The solution I am not looking for is to simply use the Arch equivalent packages or give up on Flatpaks. I want the Flatpaks to be themed properly on my system. This is not an exclusively stylistic issue either, it's also a usability one. "Snackbar"-like popups are missing backgrounds, and padding is missing in many places, both problems significantly decreasing legibility of the interfaces.

Comparison of poor legibility in broken Flatpak apps
The lack of a backdrop, drop-shadow, and padding in general makes these about dialogs particularly troublesome to read. A good example of the issue, but by far not the only one.

Thank you in advance to all help available.

seth · 2025-05-14 06:19:10

I'm assuming this is most likely an issue with my Arch system and not Flatpaks in general, as Flathub screenshots display properly themed GTK4 applications that upon installing on my system, look nothing like these screenshots

Flatschpaks cannot just use host stuff. You'll have to provide the theme by either flatpak installing it or (punching more holes into the entire sandbox illusion by) allowing the flatschpak access to the host installation and need to direct it to use it by exporting the relevant GTK_THEME to its environment or likewise allow the flatschpak access to your ~/.config/stuff

Random screenshots aren't proof of anything but illustrate the system configuration of the individual who took the screenshot and will most certainly not reflect the particular configuration on your system.

Have you btw. tried to simply google this incredibly common question?
I get ten pages and (I cannot believe I'm writing this but) a decent AI response…

someUser · 2025-05-14 06:39:29

Most likely, the problem is that the flatpak version uses Gtk 4.16, while the Arch Linux version is using Gtk 4.18. See also https://github.com/flathub/com.rafaelma … 3007298398

seth · 2025-05-14 07:13:18

If this is only about a "dated" adwaita theme, yes. Otherwise you cannot just use custom themes in flatpaks regardless of the used gtk version.

77Z · 2025-05-15 00:43:13

I understand that flatpaks run in their own Linux namespace and cannot use outside themes. I have no interest in any custom theming beyond getting the GTK4 theme to look as it should in these flatpaks.

Random screenshots aren't proof of anything but illustrate the system configuration of the individual who took the screenshot and will most certainly not reflect the particular configuration on your system.

This isn't exclusive to the example app (Blanket) I provided. Every GTK4 application installed from flathub has these issues and looks nothing like the screenshot provided. I also understand that screenshots are not the best metric to understanding this issue, but when every single GTK4 flatpak looks scuffed compared to the screenshots on flathub, I can only assume that this is not what they're supposed to look like.

Have you btw. tried to simply google this incredibly common question?

Yes. Of course. This forum is my last resort because I don't understand what is happening here, and many days of googling has not provided me any help.

I understand your distaste for flatpaks as well, and I apologize that I chose to use this packaging format, but at least it's not snap.

Most likely, the problem is that the flatpak version uses Gtk 4.16, while the Arch Linux version is using Gtk 4.18.

Again, this issue is not exclusive to Blanket, and this isn't a dated adwaita theme, this isn't even an adwaita theme. This is just incorrect.

seth · 2025-05-15 15:18:16

Does either of those screenshots (good or bad) your local theme?
You'd best address the author of the flatpak about how the screenshot was generated is you suspect the presented theme should be bundled w/ the flatpak.
But it's also possible that those flatpaks just come pre-configured to invoke the local config.

Arch Linux

#1 2025-05-13 23:18:13

Flatpak GTK Applications Display Improperly

#2 2025-05-14 06:19:10

Re: Flatpak GTK Applications Display Improperly

#3 2025-05-14 06:39:29

Re: Flatpak GTK Applications Display Improperly

#4 2025-05-14 07:13:18

Re: Flatpak GTK Applications Display Improperly

#5 2025-05-15 00:43:13

Re: Flatpak GTK Applications Display Improperly

#6 2025-05-15 15:18:16

Re: Flatpak GTK Applications Display Improperly

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