Hi Anania,
Did you mean that you want a blue border around the whole catalog (on this page: https://onathingemasters.com/wp/products/accessories/)
For example, something like this:

If this is what you had in mind, you can use the code below to replace what you currently have in your Catalogue’s “Custom CSS” box (on the Edit Catalogue page):
.prod-cat-inner,
.prod-cat-container {height: auto!important;}
.prod-cat-container {
margin: 35px 0 0 0;
border: 3px solid #80bee1;}
.prod-cat-header-div {
width: 100%;
margin-bottom: 0;
border: none;
margin: -32px 0 0 0px;
}
.prod-cat-sidebar {
width: 23%;
margin: 1%;}