message: fix(masthead): fix build error
  This change attempts to fix the build error that is observed by
  incorporating the full set of masthead styles.
  Refs
diff: @@ -180,9 +180,11 @@ $search-transition-timing: 95ms;
  }
  @include carbon--breakpoint-down(lg) {
  + .#{$prefix}--masthead__l1 {
  display: none;
  }
  }
  +}
  @include exports('masthead-l1') {
  @include masthead-l1;
  