Is there a way to add either a shadow or border around the posts that show up in the grid. These “Themes” in the style tab are somewhat limited and I’m using the paid version.
Welcome to our forum,
you can create your own theme by creating add-on for Post grid, please see the demo add-on inside plugin folder demo-addons/post-grid-addon-themes.zip you install post-grid-addon-themes.zip as plugin and this will add an extra theme under themes drop down.
Also you can filter grid items by filter hook, Please see the documentation here