Using Refined Toolkit for Confluence Cloud you can add your touch to the look and feel of the Confluence spaces.
Running Refined Toolkit you can choose from adding themes globally that your space admins can choose from, or have the space admins create themes of their own. If you're an admin, you can export a theme from one instance and import it to another one.
A space that is themed with Refined Toolkit will get a Space Home and pages will have a surrounding theme. Learn more here.