Use extends

sass/utilities/controls.sass

@@ -4,7 +4,7 @@ $control-radius-small: $radius-small !default
 $control-padding-vertical: calc(0.375em - 1px) !default
 $control-padding-horizontal: calc(0.625em - 1px) !default
 
-=control
+%control
   -moz-appearance: none
   -webkit-appearance: none
   align-items: center
@@ -31,6 +31,9 @@ $control-padding-horizontal: calc(0.625em - 1px) !default
   &[disabled]
     cursor: not-allowed
 
+=control
+  @extend %control
+
 // The controls sizes use mixins so they can be used at different breakpoints
 =control-small
   border-radius: $control-radius-small