Adding Icons to Off Menu Trigger Button

Hi guys

I would like to know if there is a filter I could use to change the icon for the Off Menu Trigger Button. I also need that same "trigger" button to change to a cross (using a custom SVG) when clicked, as I'll be positioning the overlay 130px from the top of the page to still reveal the "trigger" button. I know could probably do this with JS, but was hoping I could just use a filter or something built into GP Premium.

Any help as always will be appreciated.