Split portfolio into two collums on mobile

Site URL: https://radish-amethyst-2hws.squarespace.com/portfolio-1-1

Hi I would like my protfolio listed in two collums. I tried the below code and although It made two collums it is just listing the images underneath eachother on one side. 

password; 12345

Add to Design > Custom CSS

@media screen and (max-width:767px) {
div#gridThumbs {
    display: grid !important;
    grid-template-columns: repeat(2,1fr) !important;
    grid-gap: 10px 10px;
}
.portfolio-grid-basic .grid-item {
    width: 100% !important;
}
}