Change outline colour of contact form button

Hi,

I've recently tweaked the submit button to change colour whenever I hover over it, and wanted to make another change to it so that the outline colour which is currently black matches the grey #848484 used on the other outlines on the contact form, however currently not having any luck finding a solution.

I was wondering if anyone would be able to provide any help please? Thanks in advance

@jackmatthew Hi! Can you share your site URL for context? 

Hey! 

URL: https://www.jackmatthewpayne.com
Password: Matthew12345