If you manually modify the container size for a notebook, the Dashboard shows the Container size as "Unknown" we an error message:

Instead of saying "Unknown" the Container size could show "Custom".  Additionally, it could have some sort of hover over tool tip like the ! to show the requests and limits.

Why is this important?

"Unknown" implies that the dashboard isn't capable of querying what the size of the Workbench and there is something wrong.  But it isn't unknown and there is nothing wrong with the notebook.  It is specified in the spec of the Notebook object and can be easily accessed.