I can't get this to work though. I'm not sure what I'm doing wrong. I get a few issues:
#1
error 1 : 1 Unexpected "GM_addStyle(".
error 1 : 13 Unexpected "". error 13 : 1 Unexpected "".
error 13 : 2 Unexpected ")".
error 13 : 3 Unexpected ";".
Edit: turns out OPs code works perfectly and the ones from below just straight up don't work for me.