Bedford v7.0: Custom CSS for Changing the Icon of the Sidebar Menu

1 hour ago, Pac said:

Site URL: https://www.bloomboxus.com/what-we-do

How do I custom code to change the "+ plus icon" sidebar menu for mobile navigation? 

Having a label of the "+" would also help - I've tried exploring other ways to do so, but it's hard to find the answer and/or support I am seeking for.

The css of the plus sign is

@media only screen and (max-width: 640px) {
		.folder-nav-toggle:after, .category-nav-toggle:after {
                content: "+";
                display: block;
                text-align: right;
        }
}