Deprecated `scrollbar_thumb.background` usage

[maxdeviant]

This extension has been identified as using the deprecated scrollbar_thumb.background style property.

This property has been deprecated in favor of scrollbar.thumb.background. Please migrate to using the new property.

The following themes are impacted:

• Theme "Nuisance" is using deprecated style property scrollbar_thumb.background

[xtrasmal]

thanks! I'll pick it up.

[xtrasmal]

Fixed in; #2