[browser] Color tab item controls always light on dark. Fixes JB#43267
[browser] Color tab item controls always light on dark. Fixes JB#43267

Web pages are more commonly light than dark so always dark controls
suit these better. Alternative whitening gradient on top would
also act quite differently.

sailfishos/sailfish-browser,sailfishos/sailfish-browser,sailfishos/sailfish-browser,sailfishos/sailfish-browser,sailfishos/sailfish-browser