CSS editor not working on WP Sydney theme

Hi guys :)

When trying to use CSS editor on my webpage, the code inspector does not work properly, and no edits are saved. As you can see on the screenshot below. The code inspector recognizes the titles as .maintitle, but it does not display any information about the style.

http://jensen-dam.dk/wp-content/uploads/2016/09/Screen-Shot-2016-09-09-at-19.25.29.png

I use the Sydney theme. As I am not the technical type, I followed a tutorial on youtube by NYC Tech club (https://www.youtube.com/watch?v=8nmZNfHZIEI), from whom I imported several features (most of them from SiteOrigin). I do not know, if these are the reasons, for the CSS Editor not working.

Hope you can help me,
Kind Regards
Rikke

p.s. I did try to deactivate the plugins one by one, that does not work…