div {
    background: url(https://example.com/image.png);
    background: URL(https://example.com/image.png);
    background: \URL(https://example.com/image.png);
    background: url("https://example.com/image.png");
    background: url('https://example.com/image.png');
    background: URL('https://example.com/image.png');
    background: \URL('https://example.com/image.png');
    background: url(data:image/png;base64,iRxVB0);
    background: url(#IDofSVGpath);

    /* A <url-modifier> is either an <ident> or a functional notation. */
    background: url("//aa.com/img.svg" prefetch);
    background: url("//aa.com/img.svg" foo bar baz func(test));
    background: url("http://example.com/image.svg" param(--color var(--primary-color)));

    background: url();
    background: url("");
    background: url('');

    --foo: "http://www.example.com/pinkish.gif";

    background: src("http://www.example.com/pinkish.gif");
    background: SRC("http://www.example.com/pinkish.gif");
    background: src(var(--foo));
    background: url(   https://example.com/image.png   );
    background: u\rl(   https://example.com/image.png   );
    background: url(   
                    https://example.com/image.png   
    );
    background: url(


https://example.com/image.png


);
    background: URL(https://example.com/ima\)ge.png);
}