Column problem

Hello,

I want to use the “Post-Grid” Plugin to show 2 Cols Blog Posts. I have inserted the shortcode into one Page. But instead of 2 Col’s, all Posts are shown only in 1 Col.

I checked the console and I think the Issue comes from: item mix skin even flat
Screenshot of the Issue
Screenshot of marked Container

I added following code but it doesn’t help:

.post-grid.grid {
	width: 100%;
	margin: 0;
	float: none;
}