We will review both of the UI libraries below.
To use jQuery UI, you must link to the library after first linking to the standard jQuery library. As with jQuery, you can link to the jQuery UI library either via a hosted CDN (from Google or jQuery) or by downloading and hosting the library yourself.
Note that jQuery UI is themeable: you can use the stock themes (a pre-designed set of CSS rules that govern how popup menus, buttons, and other elements look in response to user interactions) or build your own themes with jQuery UI's ThemeRoller.
jQuery UI's ThemeRoller gives you a visual tool to set styles for just about any aspect of jQuery UI-produced elements, from header color to rounded-corner radius size to drop shadowing. To use it, visit jqueryui.com/themeroller: