CSS Radio Buttons

Can anyone point me to the CSS code where the Radio buttons are formatted?

I am using a child theme and the radio buttons have gone funny. They are barely visible but when you click down it goes normal again! and then when you release the click the tick comes right out of the box and the box disappears.

Not sure how this happened as I haven’t edited anything to do with them (I don’t think) I’m pretty confident with CSS but never worked with radio buttons before.

Thanks in advance.