a {
    background-image: url(data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7);
    background-image: url("./image (1).jpg");
    background-image: url('./image (1).jpg');
    background-image: URL('./image (1).jpg');
    background-image: url(   './image (1).jpg');
    background-image: url('./image (1).jpg'   );
    background-image: url(   './image (1).jpg'   );
    background-image: url(   
    './image (1).jpg'   
    );
    background-image: url();
    background-image: url(   );
    background-image: url("");
    background-image: url(   ""   );
    background-image: url('');
    background-image: url(   ''   );
    background-image: url(   ' '   );
    background-image: url(./image.png);
    background-image: url(   ./image.png   );
}