It's due to line 44 in your "rnshop-custom.css", where it says
.hikashop_subcontainer {
min-height: 248px !important;
min-width: 248px !important;
position: relative;
}
Whoever set the min-height, might have done so with best intentions due to the greatly varying length of product names, but there's a better way of doing so: Set min-height for the product name only, not the entire (sub)container.
BTW, the present min-width property setting also hampers the display at certain browser widths, causing the containers to overlap instead of resizing.
So, you may want to review and rework the custom CSS accordingly, eventually with the help of media queries if certain browser widths require.