Usage of "Rather"

I'm a bit of crossroads which one is to use. Here's an example:
-You're behaving rather strange; or
-You're behaving rather strangely;
I'm not sure which one is correct or maybe these two are both correct. Nonetheless, here's another example:
-He was looking rather condescending at me; or
-He was looking rather condescendingly at me;

If you're modifying a verb, you use an adverb, such as "strangely" or "condescendingly".

If you're modifying a noun, you use an adjective, such as "strange" or "condescending".

The addition of "rather" doesn't change these rules. It's an adverb that can modify another adjective or adverb.

Since "looking" and "behaving" are verbs, you should use the adverb after "rather".

The correct sentence: He was looking at me rather condescendingly

It’s also correct: He was looking rather condescending. But it describes how he was looking.