Removal of grey lines when using PageBuilder plugin

I’m using the Unite them with SiteOrigin’s Page Builder plugin. When I create sub-divided text blocks, I get this very light grey border around each block.

See below-

How do I disable this grey “border”?

Tried a few custom CSS entries I found on this support forum but none seem to work. It’s likely I was modifying the wrong element.

There is some very light box-shadow around these elements and you can remove it by using the following code.

.panel-grid-cell .panel {
  box-shadow: none;

Add this code to Theme Options - Other - Custom CSS

Worked like a charm! Thanks much, Aigars!