.leaflet-control-switch-view a {
    background:#fff url(map-switch-view.png) no-repeat 0 0;
}

@media
(-webkit-min-device-pixel-ratio:2),
(min-resolution:192dpi) {
    .leaflet-control-switch-view a {
        background-image:url(map-switch-view-2x.png);
    }
}