Simple and quick way to add fallback image in Oxygen Builder Classic
If you have a hero section that is playing a video background, and you are facing issues about it where it shows empty background when video is not loaded yet, this is the CSS solution that will help you solve the problem.
background-image: url('imageurl.jpg');
background-size: cover;
background-position: center;
position: absolute;
inset: 0;
z-index: 1;
transition: opacity 0.5s ease;
Just copy the code above, and while the section is active go to advanced and paste it inside Custom CSS. make sure you replace the imageurl.jpg to your actual image background fallback.
That's it.