This has been on the ToDo list for a while - I've not figured out a good way to make the layout editing page easy to use.

In the meantime you can add this CSS to your template's custom CSS file

.categories-list > div {

  width: 32%;

  float: left;

  margin-right: 1%;

}

.categories-list > div:nth-child(3) {

  margin-right: 0%;

}



@media (max-width: 768px)  {

  .categories-list > div {

  width: 49%;

  float: left;

  margin-right: 1%;

}

.categories-list > div:nth-child(2) {

  margin-right: 0%;

}



}

This will put your categories in 3 columns with a small space between them. And on narrow devices it will revert to 2 columns