Rename `.gl-label-text-black` => `.gl-label-text-dark`
We currently have gl-label-text-black
and gl-label-text-light
We should have gl-label-text-dark
and gl-label-text-light
alternatively gl-label-text-black
and gl-label-text-white
We currently have gl-label-text-black
and gl-label-text-light
We should have gl-label-text-dark
and gl-label-text-light
alternatively gl-label-text-black
and gl-label-text-white