Credit and debit card icons not showing properly

Hello, I contacted the developer of the Square payments plugin about this problem and they said to contact you instead as my issue is being caused by the theme, When I get to the checkout the square iframe only displays Amex and fails to display Mastercard and Visa logos. Is there any chance someone could have a look for me please and tell me how to fix it?

Thanks in advance

Simon

The page I need help with: [log in to see the link]