body.login {
    background-color: #111;
    font-family: 'Montserrat', sans-serif;
}
.login h1 a {
    background-image: url('https://smgedge.com/path-to-your-3d-logo.png');
    background-size: contain;
    width: 100%;
    height: 80px;
}

/* Admin Login Branding */
body.login div#login h1 a {
    background-image: url('<?php echo get_template_directory_uri(); ?>/assets/logo.png');
    width: 100%;
    height: 80px;
    background-size: contain;
    background-repeat: no-repeat;
    padding-bottom: 30px;
}