OK, I see the background is the container, the .structItem appears to be transparent, so give the container the page background and the item its own (e.g. white) background.
But then it makes mostr sense to lose the border of the block container. (or you could just remove left and right if you like.
This might be the best I can do with my limited skills
Code:
.block-container
{border:0}
.structItemContainer
{background:@xf-pageBg;
border:0px}
.structItem
{background:#fff;
margin-bottom:10px;
border-radius:10px}
You can now add a border radius to .structItem