Change Grid Loop from 3 Columns to 2

I’m trying to change the way the grid loop is displayed on my homepage from 3 columns to 2. I’ve tried the following custom CSS, but it won’t work for some reason.

/* Vantage Grid Loop Article Width */
.vantage-grid-loop article {
width: 50% !important;
}

Help?

My site is http://FOXYOXIE.com.