Can you please tell me what this css element is and video issue?

Trying to figure out what this element is for on my site
WP Audio Containerbody .mejs-container

It appears on mobile phone view to go way off out of view of the device and no idea what its for.

Also, the video background is not playing in the phone view.
It does, the video does play in preview mode using CSSHero a software program/plugin for adjusting CSS on wp sites but doesnt on an actual phone.

Any help/advice is greatly appreciated.