#map_canvas {
    width: 521px;
    height: 319px;
}


    #map_canvas .centerMarker {
        position: absolute;
        /*url of the marker*/
        background: url(marker.png);
        /*center the marker*/
        top: 50%;
        left: 50%;
        z-index: 1;
        /*fix offset when needed*/
        margin-left: -10px;
        margin-top: -34px;
        /*size of the image*/
        height: 34px;
        width: 20px;
        cursor: pointer;
    }

@media (max-width: 991px) {
    #map_canvas {
        width: 100%;
    }
}