cesium_example_auth/public/cesium_example/lib/mars3d/thirdParty/geolocation/Geolocation.css

.tracking-activated,
.tracking-activated:hover{
    background: #0074D9 url(img/GPS_on.png);
    background-size: cover;
    background-position: center center;
    background-repeat: no-repeat;
}

.tracking-deactivated,
.tracking-deactivated:hover{
    background-image: url(img/GPS_off.png);
    background-size: cover;
    background-position: center center;
    background-repeat: no-repeat;
}