User @import in local plugin

Hi guys! I need some help
i have a local plugin with a style.css on root folder and I need import some css libraries from other folder (assets), 
When I load my plugin all import files give me 404 error.

how I can do it?
@import url('/local/myplugin/assets/file.css'); no work
@import url('./local/myplugin/assets/file.css'); no work
@import url('./assets/file.css'); no work
@import url('assets/file.css'); no work

please can help me?