Remove Basemap even when "No Basemap" is selected (see image)

[JamesOLoughlin]

I need to use Cesium's terrain and data. Overlaying Arc Online vector tile layers but there is a fill that is rendering. Using Extents doesn't seem to be a viable option visually. Is there a way to remove the fill as seen in the image below. I have "No Basemap" selected. Is there something required to edit the data itself to solve this problem.?