Changing "Sign-In" text in Navigation?

Site URL: https://www.trubarre.org

Hello!
I'm trying to change the sign-in text that is associated with logging into member area accounts on the site. 
I tried placing the code below into the design/custom css, but it does nothing to the site?
I'd appreciate any help 🙂

.Header-account span.unauth {
    visibility: hidden;
}
.Header-account span.unauth:after {
    visibility: visible;
    content: "Online Sign-In";
    font-size: 15px;
    color: white;
    font-family: monospace;
}