Don't round corners of tiled windows

gtk-3.0/gtk-widgets.css

@@ -3041,6 +3041,14 @@ GtkBubbleWindow .toolbar {
     text-shadow: none;
 }
 
+.tiled .titlebar {
+    border-radius: 0;
+}
+
+.maximized .titlebar {
+    border-radius: 0;
+}
+
 /* this is the default titlebar that is added by GTK
  * when client-side decorations are in use and the application
  * did not set a custom titlebar.
@@ -3114,6 +3122,10 @@ GtkBubbleWindow .toolbar {
     margin: 10px;
 }
 
+.window-frame.tiled {
+    border-radius: 0;
+}
+
 .window-frame:backdrop {
     box-shadow: 0 3px 5px 1px alpha(black, 0.5),
                 0 0 0 1px mix(shade(@toolbar_bg_color, 0.7), @toolbar_fg_color, 0.12);