Change the text displayed in the guest login button

Replace the text “new name” but be certain to leave the (‘) marks
around it.

“color: #000” is the color of the text. In this case, the text will
be black. You can change this with any hex code.

“-20px” is the relative horizontal location of the text. Play with
this value until the text sits in the center.

#login-guest span {
color: transparent !important;
position: relative;
}
#login-guest span:after {
content: 'Join Us!';
position: relative;
color: #fff;
left: -20px;
}

To know how to edit web CSS, click this link.