Bugzilla is not the best forum for questions. I recommend #gnome-design on irc

I don't get what the issue is, would you provide a screenshot?
Maximized windows corners are not squared here.

ehm, I wanted to mean, "are not *rounded* here"

My original problem was because I have added custom css in gtk.css:
decoration { border: 6px ...; }

Then this border had rounded corners, but since Adwaita does not set border this probably is not bug. But most likely it would not hurt to add also:
.maximized decoration { border-radius: 0; }

There already is .fullscreen decoration and .titled decoration that resets rounded corners.

Not related to my original problem, but:
- gedit has rounded corners when maximized
- gnome-software has top right corner rounded when maximized

This is with gtk-3-20 branch.

Well, even if nothing visible changes it's formaly more correct to have the decoration node following the window shape. Thanks for spotting the other two bugs, anyway next time please file individual bugs please.

Fixed in both master and gtk 3.20 branch, commits 8ee4e45f8a9ded46aa02f0f7bc8cd8267d7d4399 and c961962ce66cc5a2d3e25f6503017f3c3351b6fa respectively.

(In reply to Lapo Calamandrei from comment #2)
> I don't get what the issue is, would you provide a screenshot?
> Maximized windows corners are not squared [sic: rounded] here.

Is it, then, intentional that if one has the Top Bar visible - as everyone does until they install a plugin to autohide it - that IT has rounded corners, and those corners are stacked above windows, including maximised ones, making said windows _seem_ to have rounded corners?

(In reply to db0451 from comment #6)

nvm, it is:
https://bugzilla.gnome.org/show_bug.cgi?id=747246