After a lot of very much appreciated help, I have managed to get my video to work, close and be responsive in a popup window.
The only issue I have not is that the little x icon to close the window is very difficult to see on desktop and impossible to see when on a mobile. The contrast with the back-round color makes is almost invisible.
Is it possible to replace this icon with an image or text and choose the color.
I have tried inserting a close window link in both html and java script into the popup content but none of them will close the window.