It’s a smooth cross-browser input library for customizing all of your form’s inputs. Dropdown selects, radio buttons, ranges, number sliders, file uploads, everything.
You can see a full demo of all elements on the main site along with a download link. This whole library runs on jQuery because it also supports custom behaviors for select fields and toggle inputs(radios/checkboxes).
If you’re looking for a truly customized checkout form then you have to try JCF. It’s available for free on GitHub and supports all major browsers including IE 8+.