Video – lightbox background

Hey creativeopole,
Sorry for the late reply, I’m not sure what you mean by the ” video background to be full width and height before clicking and opening in the lightbox” but you can make the lightbox almost full width and height with this css.
Please try this code in the General Styling > Quick CSS field or in the WordPress > Customize > Additional CSS field:

div.mfp-iframe-scaler  {
  height: 100vh !important; 
  width: 100vw !important;
  }
.mfp-iframe-scaler iframe {
    left: -15vw !important; 
    width: 90% !important; 
    height: 90% !important; 
}

After applying the css, please clear your browser cache and check.
Is that what you meant?

Best regards,
Mike