Squarespace - make full size banner automatically fill screen

Hi, I have some Squarespace sites that have full-size banner images on the landing screen, however, the height of them compared to browser size changes with every browser / size of browser. Is there any code to put into the sites to make the banner images automatically fill up the screen, so it doesn't show borders of the below content on different screens?

Can you share an example? Screenshot? URL?

How have you got these sections set up currently?

1 minute ago, Ziggy said:

Can you share an example? Screenshot? URL?

How have you got these sections set up currently?

It's all of my websites. They are designed as sections with a a regular background image or video. But they are never full screen on all devices - unless I take so many fluid engine boxes that it covers for all browsers but then it's far too many for other browser sizes.. There should be some code that automatically sets the first section to 100% page height, no? 

9 minutes ago, charlineca said:

There should be some code that automatically sets the first section to 100% page height, no? 

Setting the section height to "L" should make the minimum height 100vh is that what you have?