Putting Image Blocks into Multiple Rows on Mobile Site

Site URL: https://www.zigzagclothing.co.uk/brands

Hi forum, 

I am trying to put these images blocks into multiple rows on the mobile site, so they appear 2x2 rather than 1x4 as they are currently:

(I have tried adding code from similar posts but has had no effect)

eg. 

Any help hugely appreciated! 

Add to Design > Custom CSS

/* Brands page mobile */
@media screen and (max-width:767px) {
div#page-section-5f770018aa294763ea4f8579 .span-12 .span-4 {
    width: 50% !important;
    float: left !important;
}
}