Compound rules in the Numbers app?

I am trying to create a set of rules in Numbers that will result in the following:

• If the cell contains a single "dash", i.e. the single character "-", it will be highlighted green
• If the cell contains any other characters, i.e. is not empty, it will be highlighted red
• If the cell is empty, it will have no highlighting

No set of rules I've entered yet has enabled this result, and I've spent a decent amount of time typing in different search strings into my search engine with zero luck so far... :(

Is it possible to get this result? And if yes, how?

Thanks!