How to override your global Theme Design on a specific page or blog post
Login to the CMS.
On the left-hand side, in the tree menu, go to any page or blog post.
Go to the tab, 'Advanced'.
Locate the label 'Override design style'.
You will now see a button labelled 'Add', please click this.
From the slide-out panel on the right, select a theme design for this page or blog post.
In the bottom right corner, click 'Save and publish'.
Your page or blog post will now be displaying a completely different Theme Design to the rest of your website.