Changing the Number of Product Thumbnail Columns

Hi,

I am using woocommerce with the Virtue Theme. For the last couple months I have been using this css to make the product thumbnails line up in 5 columns:

div.product .product_thumbnails > a {
	display: block;
	float: left;
	width: 20%;
}

I got that css straight from this support thread: https://www.ads-software.com/support/topic/woocommerce-gallery-has-not-spacing?replies=6

I just upgraded to version 3.5.0 today and now my product thumbnail images are back to rows of three, without any off the css changing. How do I fix this?

Thank you