I would like to suggest an option to customize the highlight color of the active tab. For example, users could select an accent color in Opera’s appearance settings that is used for the currently selected tab.

This would make the active tab instantly recognizable instead of having to visually search for the slightly different grey background.

I think this would be a useful accessibility and productivity improvement. People who regularly work with many tabs could identify their current tab at a glance, while users who prefer the existing appearance could simply keep the default setting.