How to enable jQuery UI in JSFiddle?

The UI for adding JS frameworks has been adapted (multiple times).

Currently you can add these frameworks by clicking on the settings-cog-wheel of the Javascript section:

The JSFiddle Frameworks & Extensions selection has been moved to the Javascript pane options!

New Answer

Checking the jsFiddle site today, I see they added some controls. This is in the same style of answer as reto's and dotancohen's.

I have not tested the UI portion specifically yet, but I do notice that when you select jQuery versions (edge) or 1.9.1, jQuery UI is available in the list of checkboxes that appear beneath the dropdown box.

Old Answer

Along with the other answers (I intend to complement dotancohen's answer) discussing that pretty significant JSFiddle UI change, I wanted to finish the information by saying jQuery UI specifically was not an option for me. I had to go into "External Resources" on the left-hand side and enter these URLs as well:

https://ajax.googleapis.com/ajax/libs/jqueryui/1.11.4/jquery-ui.min.js https://ajax.googleapis.com/ajax/libs/jqueryui/1.11.4/themes/smoothness/jquery-ui.css

Example jQuery UI JSFiddle