div {
  background: url(/images/bg.png);
  background: -fb-url(/images/bg.png);
}

@font-face {
  src: url(RobotoFlex-VariableFont_GRAD,XTRA,YOPQ,YTAS,YTDE,YTFI,YTLC,YTUC,opsz,slnt,wdth,wght.ttf);
  src: url(foo.ttf?query=foo,bar,);
  src: url(foo.woff2?foo=rgb\(255,255,0\));
}

a {
  content: url(https://example.com/\)\).jpg);
  content: url(https://example.com/\(\(.jpg);
  content: url(https://example.com/\ \ .jpg);
  content: url(   https://example.com/\)\).jpg   );
  content: url(   https://example.com/\(\(.jpg   );
  content: url(   https://example.com/\ \ .jpg   );

  background:
    no-repeat url(https://example.com/\)\).jpg),
    no-repeat url(https://example.com/\(\(.jpg),
    no-repeat url(https://example.com/\ \ .jpg),
    no-repeat url(   https://example.com/\)\).jpg   ),
    no-repeat url(   https://example.com/\(\(.jpg   ),
    no-repeat url(   https://example.com/\ \ .jpg   ),
    no-repeat url(foo.ttf?query=foo,bar,),
    no-repeat url(foo.woff2?foo=rgb\(255,255,0\))
    no-repeat url(RobotoFlex-VariableFont_GRAD,XTRA,YOPQ,YTAS,YTDE,YTFI,YTLC,YTUC,opsz,slnt,wdth,wght.ttf);
  ;
}