extract .alert-variant mix-in
more nesting in button-groups.less
more nesting in navs.less
extract .label-variant mix-in
extract .progress-bar-variant mix-in
Merge pull request #8404 from cvrebert/alert-variant

extract .alert-variant mix-in
Merge pull request #8405 from cvrebert/button-groups-nesting

more nesting in button-groups.less
Merge pull request #8406 from cvrebert/navs-nesting

more nesting in navs.less
Merge pull request #8407 from cvrebert/label-variant-mixin

extract .label-variant mix-in
Merge pull request #8408 from cvrebert/progress-bar-variant-mixin

extract .progress-bar-variant mix-in