Ignoring system-wide mouse settings by Logitech Options
It appears that Vivaldi doesn't honor system-wide settings specified by Logitech Options. I cannot use the "back" and "forward" actions assigned to mouse scroll wheel's left and right tilts, respectively, while this works, e.g., in Safari and Firefox. Please verify and file a bug, if needed.
OS X 10.11.6, build 15G1212
Device: Logitech M535 (Bluetooth)
Logitech Options v.6.35.142