How to get native windows decorations on GTK3 on Windows 7+ and MSYS2

You can set GTK_CSD=0 environment variable to disable client-side window decorations and enable Windows native decorations, which gets rid of the ugly win7-like titlebar, as well as Adwaita-like one.

Thera are two sub-problems: missing icons and setting right theme.

Missing icons

For missing icons it was enough to copy these icons

• window-close-symbolic.symbolic.png
• window-maximize-symbolic.symbolic.png
• window-minimize-symbolic.symbolic.png

from: C:\msys64\mingw32\share\icons\Adwaita\22x22\actions

to: "your executable folder"\share\icons\Adwaita\22x22\actions

Theme

Using win32 native theme

There is actually a built-in native-like theme in GTK3. For using native-like theme just create file "your executable folder"\etc\gtk-3.0\settings.ini with this in it

[Settings]
gtk-theme-name=win32

win32 theme is built in into GTK3 and only three icons from previous step seems to be needed.

On windows 7 this looks as following:

The problem is, that the decorations looks the same even on Windows 10 (including window decorations).

From comment from @andlabs : GTK+ 3 uses the uxtheme.dll APIs to get its Windows look and feel, and unfortunately Microsoft has kept those Windows 7-like for window borders. (more in comments)

You can see Windows 10 Gtk3 application with win32 theme here:

Using non default theme

And if you are not happy with default or win32 theme, you can use custom themes (like this Flat-Pat) from the internet. :) In order to do it you need to create config file:

"your executable folder"\etc\gtk-3.0\settings.ini with this in it

[Settings]
gtk-theme-name=Flat-Plat

and you need to copy the theme files to directory in path of your executable

"your executable folder"\share\themes\Flat-Plat

in that folder, the index.theme file and gtk-x.x folders should be present. Obviously gtk-theme-name and folder name should match.

After you run the executable you should be able to get different theme.

EDIT: So there is a win32 theme built-in, thank you @andlabs

EDIT2: Added screenshots

EDIT3: Added Windows 10 screenshot and corrected facts.