added sm border radius (#16611)

* added sm border radius

* Update ui/css/design-system/attributes.scss

Co-authored-by: George Marshall <george.marshall@consensys.net>

Co-authored-by: Garrett Bear <gwhisten@gmail.com>
Co-authored-by: George Marshall <george.marshall@consensys.net>

ui/css/design-system/attributes.scss

@@ -50,7 +50,8 @@ $font-style: normal, italic, oblique;
 $font-size: 10px, 12px;
 $border-radius: (
   xs: 2px,
-  md: 4px,
+  sm: 4px,
+  md: 6px,
   lg: 8px,
   xl: 12px,
   full: 50%,