How can I use the HTML widget and HTML item?

You can put any html code into the HTML widget and HTML item, javascripts and css codes too. The widgets are always over the slider, and aren’t moving away, so use the HTML item, if you want to have something all the time over your slider, and the item is moving with it’s slide. You can see an example in here, also you should check out that documentation, because on most of the other examples you can see these used too.