The RichText editor link feature toolbox has broken styling on Microsoft Edge.
You can see an example of this bug in the attached gif.

Steps to reproduce:
1. Start creating a new article in Microsoft Edge 42.17134.1.0
2. Type something in the RichText area (in Intro for example)
3. Highlight part of text and press link button in the RichText toolbox

Result:
The toolbox has broken styling: dark background does not fill the toolbox.