User blog comment:Rappy 4187/Technical Update: April 20, 2015/@comment-1192804-20150421130738/@comment-11733175-20150421213400

Actually, the correct method is:

body.skin-oasis { background-image: url('http://example.com/test.png'); background-position: top center; background-repeat: no-repeat; background-attachment: fixed; background-size: cover; background-color: #000; color: #fff; }

The quotes make no difference, and  should be avoided unless absolutely necessary.