Change Color of Button in Mobile Menu

Hello,
I'm currently working on updating this website and I need the "Contribute" button to have the same color and outline in both Desktop and Mobile views. The previous designer added custom CSS for the Desktop button. (see below), and now I need to add additional CSS for the mobile button. However, I'm not sure what selector to use for the mobile button.

/*Set Button Color */
.header-actions .btn {
color: #47166A;
background-color: #feae00 !important;
font-weight: bolder !important;
}

/*Set Button Color */
.header-actions .btn:hover {
color: #48166b;
background-color: #feae00;
}
body { 
border:0px solid #ffffff;
}

Thank you so much, Lesum, for your response. The code worked perfectly:-)