Woocommerce Place Order Button not showing

We are trying to integrate Woocommerce into our site and everything seems to be setup and working but when we get to the checkout the Place Order button is just showing as white.

I’ve tried deactivating all the plugins except Woocommerce and that doesn’t sort it. Our theme is up to date as are all plugins and WordPress.

If we click the white space to place an order it goes through ok. I’ve tried setting the theme to twenty-fifteen and the button displays fine.

Has anyone else experienced this?

Can be seen at http://www.hhenvironmental.co.uk/shop/

Any help greatly appreciated.