Add $input-border-width; refs #18150

scss/_custom-forms.scss

@@ -138,7 +138,7 @@
   background: #fff url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAUCAMAAACzvE1FAAAADFBMVEUzMzMzMzMzMzMzMzMKAG/3AAAAA3RSTlMAf4C/aSLHAAAAPElEQVR42q3NMQ4AIAgEQTn//2cLdRKppSGzBYwzVXvznNWs8C58CiussPJj8h6NwgorrKRdTvuV9v16Afn0AYFOB7aYAAAAAElFTkSuQmCC) no-repeat right .75rem center;
   background-image: none \9;
   background-size: 8px 10px;
-  border: 1px solid $input-border-color;
+  border: $input-border-width solid $input-border-color;
   // Use vendor prefixes as `appearance` isn't part of the CSS spec.
   -moz-appearance: none;
   -webkit-appearance: none;

scss/_variables.scss

@@ -266,6 +266,7 @@ $input-bg-disabled:              $gray-lighter !default;
 
 $input-color:                    $gray !default;
 $input-border-color:             #ccc !default;
+$input-border-width:             $border-width !default;
 $input-box-shadow:               inset 0 1px 1px rgba(0,0,0,.075) !default;
 
 $input-border-radius:            $border-radius !default;