Foundation UI elements refer to common interface elements such as the menu, sharing bar, or close buttons. These are application components that have received a heavy investment of resources to be produced. 

These elements are technically very complex to change, and any modifications to them also introduce changes to interaction which has been meticulously designed to promote engagement and increase revenue

The style of these elements on the other hand, are modifiable. Because Marfeel uses CSS, hooks and extension points are in place to perform the changes a customer may want to introduce.