Update values to make linter happy

Author: fredden

app/design/adminhtml/Magento/backend/web/css/source/_actions.less

@@ -446,12 +446,12 @@ button {
             }
 
             &::after {
-                border-color: transparent transparent transparent #000;
+                border-color: transparent transparent transparent @color-black;
                 border-style: solid;
-                border-width: 0.4rem 0 0.4rem 0.5rem;
+                border-width: .4rem 0 .4rem .5rem;
                 content: '';
                 height: 0;
-                margin-top: -0.2rem;
+                margin-top: -.2rem;
                 position: absolute;
                 right: 1rem;
                 top: 50%;