Doesn't respect default system theme on Ubuntu

[ghost]

What should happen:

Default Ubuntu Yaru Theme should be used.

What happened instead:

Default Adwaita theme is being used but with messed up tabs:

How to reproduce:

1. Install Ubuntu 22.04
2. Install Tootle through flatpak install tootle (assuming you have already set up the flathub remote)
3. Launch

Screenshots (if applicable):

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Build context:

• Distro: __
• App version: __
• Build type: Flatpak / Built from source / Built by a third-party maintainer

Logs:

(Terminal logs are often invaluable. If you can, launch the app from terminal with com.github.bleakgrey.tootle and paste the output here)

Additional info (if needed):

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[harmathy]

Try installing org.gtk.Gtk3theme.Yaru via flatpak.