Skins have been deprecated since version 3.0.0 released on September 3, 2015. The theme has enough settings to allow you to create a design that fits your needs without loading extra bloat. If you select the "base" skin this admin panel will be removed and you will see an error message. To re-enable please visit the online snippets for this theme.
We highly recommend you select the BASE skin and make all your edits via the Customizer to get the design you want or use a child theme (both are more optimized methods).