Style issue with check boxes in contact form 7

I’m trying to style the check box border of a contact form 7 form on this page http://sunbeamsdaynursery.com/enquire/ and for the life of me cant do it!

In the Inspect Element part of Chrome Developer tools I can see the exact bit of CSS i need to change and changing the border colour here from white to black updates in real time but I cant seem to replicate it in the actual css file on the server. The path is (index):412 and I see this refers to some inline css in the index file but how do I access this CSS to edit the border colour to black?

https://wordpress.org/plugins/contact-form-7/