Merge pull request matplotlib#22607 from greglucas/macosx-button-theme

ENH: Add dark/light mode theme to the buttons

Author: timhoffm

src/_macosx.m

@@ -873,6 +873,9 @@ -(void)save_figure:(id)sender { gil_call_method(toolbar, "save_figure"); }
         NSImage* image = [[NSImage alloc] initWithContentsOfFile: filename];
         buttons[i] = [[NSButton alloc] initWithFrame: rect];
         [image setSize: size];
+        // Specify that it is a template image so the content tint
+        // color gets updated with the system theme (dark/light)
+        [image setTemplate: YES];
         [buttons[i] setBezelStyle: NSBezelStyleShadowlessSquare];
         [buttons[i] setButtonType: buttontypes[i]];
         [buttons[i] setImage: image];