@jorovats it's CSS, it tells the browser how to display content from that site - in this particular case, to hide it. That is the ad blocker hiding ads from those sites, not actual links to any of those sites.
I wonder if this has a name
Like sgunhouse said, it is code injected by Opera Adblocker to hide ads.
and if it has a solution,
You can disable Opera Adblocker, likely you will get rid of this stylesheet then also.
Oooh I see, thanks for helping me, I learned something new