@unknown {}
@unknown url(image.png) {}
@unknown url(   image.png   ) {}
@unknown url("image.png") {}
@unknown url(   image.png   img   ) {}
@unknown url(   image.png"" img   ) {}
@unknown url(   image.png\ img   ) {}
@unknown url(   image.png\)   ) {}

@unknown;
@unknown x;
@unknown x{}
@unknown x {}
@unknown{}
@unknown{a: b; c: d;}

@unknown x ( a + b ) ;
@unknown x ( a - b ) ;
@unknown x ( a , b ) ;
@unknown x( a , b ) ;
