Chore/UI styles

[nathanwoulfe]

Noticed when scrolling content or datatype views in vertical layout the editor was visible behind the header. These changes add a background to the header and a pseudo-element to mask overflow.

Also tightens whitespace in workspace-property-layout to ensure even whitespace above and below all instances (reduces padding when element is in a content node as the containing box adds padding-Y).

Finally, tweaks TinyMCE styles to match editor borders from UUI - ie squared corners, color, border width.

[nielslyngsoe]

Hi @nathanwoulfe I really love your focus on the details and love your effort to bring everything to a production ready quality.
I do though have a bit of comments on the way these have been carried out. And I hope you will appreciate my corrections, as learning into how we separate concerns with Web Components, more specifically Shadow DOM.

I hope my comment in the code will survive though I will be correcting the code as well. :-)

[nielslyngsoe]

@nathanwoulfe
Please read my comments, see the changes I made, and check if you are happy with the PR.

I disabled auto-merge so you can approve it this way. And I have approved the PR. So Just merge if you are happy :-)

[nathanwoulfe]

Thanks Niels, that all makes sense - appreciate your holistic view of how this all works together 😄