Responsive navigation button not working

My responsive navigation look good on a desktop but on a phone the button does not look like it should for a navigation can I please have some help. This is what my navigation looks like on codepen which looks good on a phone and on a desktop.
This is the codepen link https://codepen.io/owainbennett10/pen/wvKparx

This is the website so far with the navigation included http://siondafydd-com.stackstaging.com/.

Can you please help me solve the problem

A post was merged into an existing topic: Responsive Navigation