Merge remote-tracking branch 'twbs/v4-dev' into v4-dev

scss/utilities/_background.scss

@@ -2,10 +2,6 @@
 // Contextual backgrounds
 //
 
-.bg-inverse {
-  background-color: $brand-inverse;
-}
-
 .bg-faded {
   background-color: $gray-lightest;
 }
@@ -19,3 +15,5 @@
 @include bg-variant('.bg-warning', $brand-warning);
 
 @include bg-variant('.bg-danger', $brand-danger);
+
+@include bg-variant('.bg-inverse', $brand-inverse);

scss/utilities/_flex.scss

@@ -8,6 +8,7 @@
     @include media-breakpoint-up($breakpoint) {
       .flex-#{$breakpoint}-first { order: -1; }
       .flex-#{$breakpoint}-last { order: 1; }
+      .flex-#{$breakpoint}-unordered { order: 0; }
     }
 
     // Alignment for every item