woocommerce update and edit css

Hi,
Ive just updated woocommerce and didint realise i’d updated some css when i first installed (changed some colour on the checkout pages) now i can’t seem to find where in the style sheet to edit the css again. to change the colour from white to black. been looking for days now and tried everything to find it. any help much appreciated.

its the checkout box that allows you to select your payment method type ie paypal card etc..