Is there any way to hide the banner wide area?

I’m using the Banner Wide widget area to display my header pic in order to be able to make it only visible on certain pages, but on pages where the image is hidden, the banner area is still shown as a big wide brown-coloured space with nothing in it. Is there a way to get rid of this, or at least adjust the height of the area so that it doesn’t take up such a large part of the screen?

Banner pic visible: https://www.way2japan.com/
Banner pic hidden: https://www.way2japan.com/about-waytojapan