All pop-up pages are full width

Since begin of the week all the pop-up pages ( including the login dialog ) are full width. ( I've deleted my browser history ) Checking css via the element inspector of Chrome there is now always on top. Where comes this from?
1 answers

Should something in CSS, deleted my theme and restore a backup. For my it is solved. How it happend? I don't know. I didn't modify nothing in the css since the backup.