Markdown Previewer Weird divs

Hi guys,

I am building the Markdown Previewer with React and Redux at the moment. However, I have a huge problem when testing it in Safari. When I click on the textarea, there are suddenly new, weird div-Elements above and below the body.

This is how it should look:

This is how it looks after clicking the textarea:

Here is my code on Github:

Your browser information:

User Agent is: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/11.1.2 Safari/605.1.15.

Link to the challenge:

I am getting closer to the problem zone. Somehow determing the width of creates these divs