With the ButtonFacade ( Masque ) plugin you can change the appearance of action buttons and icons.
/ bf with command
You can enter the settings of this plugin and select the skin you want. Also, from the Addons tab in the settings of this plugin, you can apply different skins separately on different action bars.
This plugin, because version 3.3.5 is no longer available, has been provided to you as a direct link and you can download it with 15 skins .
If you care about the look of your user interface, you can greatly customize it with this plugin.