Fix bug where border-1, border-2, etc don't work (#1526)

src/scss/_utilities.scss

@@ -1,5 +1,5 @@
 $border-values: (
-  null: $border-width var(--#{$prefix}border-style) $border-color-translucent,
+  null: var(--#{$prefix}border-width) var(--#{$prefix}border-style) $border-color-translucent,
   wide: $border-width-wide var(--#{$prefix}border-style) $border-color-translucent,
   0: 0,
 );