Template:Styles/add blackHorizontalLogo.css

/* Additional styles, call with 'style2' parameter */

#p-logo a {
    background: url(https://upload.wikimedia.org/wikipedia/donate/6/60/Wmf_logo_horiz_K.svg);
    background-repeat: no-repeat;
    background-position: center center;
}

@media screen and (max-width: 981px) {
    #p-logo a {
        width: 240px;
        margin-left: 1em;
    }
}