Using Design Skins
Design skins allow you to design and edit once and have your changes update all instances across your site utilizing the design skin. They can be thought of as global design templates.
Design skins are configured in the Site Settings panel, under Element Design Skins.
These two buttons use the "Action" Button Design Skin:
That "Action" Button Design Skin can be configured in the Site Settings:
And here we can see how editing that site-wide Element Design Skin changes the design of both buttons utilizing the Design Skin. Any button, whether on the current page or not, utilizing that Element Design Skin is then modified in a single action.