remove shadow

src/client/styles/scss/molecules/slack-notification.scss

@@ -18,8 +18,11 @@
   }
   // height settings for slack button's responsive design
   // in the input and form-control element
-  .grw-form-control-slack-notification {
+  .grw-form-control-slack-notification.form-control {
     height: $input-height-slack;
+    &:focus {
+      box-shadow: none;
+    }
   }
   .grw-input-group-slack-notification {
     height: $input-height-slack;