MAGETWO-42871: Storefront menu UI issues on mobile

Author: zanilee

app/design/frontend/Magento/blank/web/css/source/_navigation.less

@@ -125,14 +125,18 @@
 
         .header.links {
             .lib-list-reset-styles();
+            border-bottom: 1px solid @color-gray82;
             li {
-                border-top: 1px solid @color-gray82;
                 font-size: 1.6rem;
                 margin: 0;
                 &.greet.welcome {
+                    border-top: 1px solid @color-gray82;
                     font-weight: 700;
                     padding: 8px 20px;
                 }
+                > a {
+                    border-top: 1px solid @color-gray82;
+                }
             }
             a,
             a:hover {