Hero Top Margin does not have white background color

Hi,

I've created a website with a hero. This hero has an image set as background. I want to have approx. 20 px space between hero and menubar, so I added a top margin (20 px). But these 20 px are not white, but rather some sort of lightgrey, which is not desired. There is no background color set for this container. Changing this does not effect the outcome.

How do I get this bar to be shown as white? (In order to avoid workarounds such as an empty container)

Thanks and cheers.