No max-width for content modal windows

Problem/Motivation

When writing text in a ME text editor, there is no max-width on the modal. So the modal grows with the user

Screencast showing the text modal expanding full width of the screen: https://share.cleanshot.com/m62fZ2h5

Proposed resolution

stick to a width of the modal window and don't let it grow with content. It should grow with the window size (be responsive if the screen gets smaller) but shouldn't be wider than about 860px to be in line with WCAG line length guidelines