mechk

I don’t think the issue has to do with how I apply the code. I activated the default theme (twenty fourteen) and applied

#secondary {
	background-color: #fff !important;
}

to style.css in the theme folder (not child-folder) and still have the same problem.

It might not have been clear in my original post but the problem is only with long posts/pages or when you have several pages/posts after each other.

It just seems like the sidebar is devided in separat divs where one part is #secondary and another part something else.

Twenty fourteen, thought that was obvious from the tags, my bad.