Hi perknh,
I found the issue: it's related to nvidia proprietary drivers! (I suspected)
Solved by using nouveau drivers, but it is just a workaround.
I'm a web developer! I use Opera to develop all of my sites and applications.
I think this issue affects many people: all of nvidia drivers I try give the same result: weird rendering.
I wonder if there's a way to better inspect this problem.
Finally, I'm in love with Opera since 2006 🙂 so I'd like to help solve this. It's a pity that many people could just switch to Chrome to solve this issue..

Hi revoluzione,

I'm glad you figured out what the problem what the problem was. And I suspect you're a gamer too --using nvidia drivers is a clue!

Yes, Opera is great, and I've been using it for years too. I wish Opera would have a secure download site such as Firefox and Google Chrome do. People look for that little green lock now when they download something. I suspect Opera would have more users if it just made that one simple change. And it is because of this, I install Opera by the command line, but I don't think many people want to bother with that! But, yeah, Opera rocks. It is my favorite browser.

Also, in regards to rendering, I still have a problem seeing the cursor in the Omnibox with many themes. That problem has not gone away for me. I once considered the problem solved because all I did was change themes in LXDE; but with Xfce, I'm noticing that I can't see the cursor with a lot of themes. I only discovered recently that this problem isn't limited to one theme at all. So I'd guess you'd say, I'm using a workaround too!

All the best,