@mixin box-shadow($shadow...){@if$enable-shadows{$result:();@each$valuein$shadow{@if$value!=null{$result:append($result,$value,"comma");}@if$value==noneandlength($shadow)>1{@warn"The keyword 'none' must be used as a single argument.";}}@if(length($result)>0){box-shadow:$result;}}}