No - You’re not missing anything. Pinegrow as of yet does not work in that manner for direct manipulation on the page. It’s hard to perceive if or when that might be possible.
Here is a relative thread from 3.5+ years ago with comments by @Matjaz.
CSS Properties — Direct user manipulation on page of basics properties — via Drag etc.
There was also talk of a Designer-centric Pinegrow app 2.5+ years ago
with comments by @Matjaz also.
• Pinegrow Offspring -- Pine Seedling -- Designer App Coming? - #5 by matjaz
• Pinegrow Offspring -- Pine Seedling -- Designer App Coming? - #91 by matjaz
Hard to tell what will be coming now that they are onto another dot trail v6.x.xxxxxx . Given the lean nature of the initial v6 the new dot releases must be bringing something worthwhile. ;–)