Change white under page banner

When I create a page in ES I can add a banner. The dimension is 940x350px but you see only the top-part of the picture.
I presume that the rest of the picture is hidden by the white under the banner.
How can I change opacity of the "white" under a banner? in Vanilla?

Thanks for your input

This section can only be seen by users with a valid subscription.
If you have a valid subscription, please login now

Support is

It is currently a weekend from where we are at. Some answers may already be available on our documentation

Rest assured that we will get back to your posts as soon as the week starts!

Your time
Stack Ideas time