ScrollBarWidget specific variables

`$gbc-ScrollBarWidget-track-color`

Color of the ScrollBarWidget track

Type: color

Default value: $rgba(219, 219, 219, 0.6)

Computed value: rgba(219, 219, 219, 0.6)

`$gbc-ScrollBarWidget-thumb-color`

Color of the ScrollBarWidget thumb

Type: color

Default value: $rgba(186,186,186,1)

Computed value: rgb(186, 186, 186)