so i have a strips inside a Header, to provide dropdown menu
but when i collapsed the strip, it still leaves a blank space on the header
can give me any solution?
You collapse only the STRIP, but not the HEADER.
Maybe this is why you get a surprised result.
Maybe you want also to collapse the header?
ANother possible issue could be, that you first have to collapse elements inside the STRIP, before collapsing the STRIP istself.