Trouble Using CSS Selector with Popup Pro

Hi there
I have just installed popup-pro on WordPress 4.6 using the Story Theme, and am having trouble getting the CSS selector to work.
The theme provides a WYSIWG interface for what you see on the homepage, and it appears as if the field they supply for the button link automatically appends the url of my site.
So using #contact, for instance, and then setting this in the CSS selector doesn't work.
I have attempted multiple variations on links and tags, including the css selector for .button, but without a # or url in the button link field, the button does not display.
Curious as to how I should be thinking to resolve this.

As you can see from the screenshot uploaded, all of the attributes of this slide are established via this interface.[image pos="0"]