New Checkout Page (4.2.1) CSS NOT Overriding

I am using Yootheme template and trying to do a CSS override for the checkout page but it is not overriding.

The CSS file for the checkout page is here: /media/com_payoplans/css/site/style.min.css

Has something happened where this style sheet is not overridable?

I am using Payplans 4.2.1

Thanks