First things first: all of the elements we might ever need in order to create a form (that is, inputs, buttons, switches, and so forth) are built by the jQuery Mobile framework on top of standard (native) HTML elements.

By creating a custom element, jQuery Mobile is thus able to provide a visually more appealing set of buttons and inputs to A-grade (and B-grade as well) mobile browsers. On lower-graded platforms (C-grade), no JavaScript or CSS is applied, and therefore plain HTML elements are used.

In a nutshell, jQuery Mobile applies its scripting to mobile devices which are known to support it and render the page correctly. Other browsers will fall back to a standard display as if jQuery Mobile was not used at all.