Change corner radius with css

[Odizinne]

Prerequisites

• [X] I performed a cursory search of the issue tracker to avoid opening a duplicate issue.

Checklist to make sure the issue is not on your end

• [X] I have made sure that I do not have multiple versions of the theme installed. Only one version should be installed in either ~/.local/share/themes or /usr/share/themes or ~/.themes
• [X] The file ~/.config/gtk-3.0/gtk.css does not exist. (If it does, backup and remove it.)
• [X] I have logged out and in again.
• [X] Dark theme only. I have enabled adw-gtk3-dark in gnome-tweaks AND set the appearance to dark in gnome-control-center
• [X] The flatpak theme is installed org.gtk.Gtk3theme.adw-gtk3 and org.gtk.Gtk3theme.adw-gtk3-dark
• [X] The app I'm having an issue with is an actual GTK3 app and is not coded using another toolkit like GTK2, GTK4, QT, etc.
• [X] I have created a new user profile without any modifications except adw-gtk3.

Description

Hello, i'm working on a little project and i would need to reduce the default corner radius for this.

Is this something achievable with css? I tried somes, but it look weird. The gnome ext rounded-window-corners give the same weird result.

.background.csd {
    border-radius: 5px 5px 0 0;
}

Border radius set to 5px in GTK4 app

Border radius set to 5px in GTK3 app with adw-gtk3

I think it might be a mutter issue, if i understand the window manager render GTK3 window decorations, but i'm lacking knowledge, so i prefer asking.

OS and version [e.g Fedora 37]

Arch

Adw-gtk3 version. Also specify your installation source. [e.g tar.xz, AUR, git main branch]

AUR git

GNOME version

44

Application name and version (If the issue is with an app.)

Any GTK3 apps

[lassekongo83]

In GTK3 the border radius is handled here: https://github.com/lassekongo83/adw-gtk3/blob/main/gtk/src/adw-gtk3/gtk-3.0/_common.scss#L1771 to line 1804. And also here: https://github.com/lassekongo83/adw-gtk3/blob/main/gtk/src/adw-gtk3/gtk-3.0/_common.scss#L4484