Settings
Name - Name of the widget. Is not shown in the store, only for administrative purposes.
HTML - Here you write/put in your HTML.
It's important to link because a faulty markup can result in serious consequences for the whole store. So important that you need to check that the code you put in is correct before you save/publish.
CSS - Here you write in the CSS for the HTML. Make sure to give all elements class names and use them for styling