My dialog has a close button instead of an X

My dialog has a close button instead of an X

When I use versions 1.11.1 of jquery and 1.11.3 of jqueryui respectively, when I create a dialog box I get no box and no X in the upper right corner. Instead, I just get my title followed immediately by a button labeled "close" and my contents floating in space below it. When I use fiddle to test this out, if I regress back to about versions 1.9, a perfect dialog box appears. There is no other javascript in use (like bootstrap for instance) so there is nothing to conflict with. What am I doing wrong?