Does anyone know of a tutorial or some skeleton code samples that allows you to build an embeddable website widget like this? From what I can see, there are 2

Does anyone know of a tutorial or some skeleton code samples that allows you to build an embeddable website widget like this? From what I can see, there are 2 iframes for the button and the hidden overlay. Clicking on the iframe button enables the overlay via some sort of iframe to iframe communication on the parent(host) page