Editing page design

Click "Edit Design"

Make edits in Dev Mode

Exit back to your split view

If you're in Developer Mode, you have almost unlimited options to edit your Page Set.

Developer Mode can be as complex as you want to make it. If you're ever stuck, just hit "CMD+K" to bring up the command palette. The command palette can jump you from style to style, or it can help you navigate pages, or even do superactions like sending pages from site to site. Visit help.the.com for more information.