Wells Template and HTML to get mobile masonry to 2 columns

My site is a Wells template and I would love to make these masonry style galleries on my site have 2 columns on mobile and tablet devices, instead of 1.  Can anyone help me with HTML that would work for this Wells template?

Example: https://www.joycoakley.com/interiors

Try this Custom CSS solution:

@media only screen and (max-width:767px) {
  div#slideshow {
    display:grid!important;
    grid-template-columns:repeat(2,1fr)!important;
    grid-column-gap:8px;
    grid-row-gap:8px;
  }
}

Hope that helps!