Reduce size of gtk CSD header bars

modules/graphical/theme/default.nix

@@ -59,10 +59,28 @@
           gtk-cursor-theme-name = "Vanilla-DMZ"
           gtk-cursor-theme-size = 24
         '';
-        gtk3.extraConfig = {
+        gtk3 = {
+          extraConfig = {
             gtk-cursor-theme-name = "Vanilla-DMZ";
             gtk-cursor-theme-size = 24;
           };
+          extraCss = ''
+            headerbar {
+                min-height: 0px;
+                padding: 0px;
+                margin: 0px;
+            }
+
+            headerbar entry,
+            headerbar spinbutton,
+            headerbar button,
+            headerbar separator {
+                min-height: 0px;
+                padding: 0px;
+                margin: 0px;
+            }
+          '';
+        };
         iconTheme = {
           package = pkgs.libsForQt5.breeze-icons;
           name = "breeze";