XF 1.5 Creating a Overlay


I make a rather special request because not having the necessary skills.

I would like to create an overlay that opens automatically when arriving on my site with the automatic reading of a video or a webm file. The video or webm file center and the rest of the overlay in black with an opacity and the presence of a button to close the overlay.

And takes in the overlay visible only to visitors.

I thank the person (s), help me in this task.