Basically, make edges look like actual uninteractable edges, completely automatically.
Download the assets that you can just merge onto your existing texture pack.
May overwrite models for gray, black, and light gray stained glass panes if you already have them.Apart from that basic look, I know there is texture packs out there that have very fancy GUIs, as such, you may enable the 'Edge Formations' option for a container, and GooP will give Custom Model Data to edges depending on the slots relative to them.
Notice how there is always a line facing the non-edge slots within the container, you can find and edit these in the GooP Container Assets downloaded from the link above
Mailbox:
NumberOfRows: 3
EdgeFormations: true
ContainerType: PHYSICAL
InherentToStructure: true
...
Intender for use with GUI Texture Packs that add extra custom details, making it possible in this example to preserve the light blue details.