Core issues related to separate editing modals

[laryn]

The following core issues show up in the separate editing modals:

• https://github.com/backdrop/backdrop-issues/issues/4863 - System dialog seems hard-coded to admin theme's CSS (also noted by @olafgrabienski in https://github.com/backdrop-contrib/paragraphs/issues/60#issuecomment-801949314)
• https://github.com/backdrop/backdrop-issues/issues/4342 - Modal popups jump to the top of the page when opened

[laryn]

I think these are at a point where it's safe to close this issue.