Do not show window title in Opera and KDE

When you want to quickly switch between Opera tabs, you need to remove common window borders.

1. go to the System Settings > Window Management > tab Window rules, press New... 
2. press on Detect Window Properties and click and drag on Opera window
3. in new window press Ok
4. in tab Appearance & Fixes add tick on No titlebar and frame, in dropdown list select Apply initially, and select Yes
5. in previous tab enter own name of rule
6. Don't forget to press Ok and in Window Rules press Apply on bottom