CSS rule to apply only if element has BOTH classes [duplicate]

Let's say we have this markup:

<div class="abc"> ... </div>
<div class="xyz"> ... </div>
<div class="abc xyz" style="width: 100px"> ... </div>

Is there a way to select only the <div> which has BOTH abc and xyz classes (the last one) AND override its inline width to make the effective width be 200px?

Something like this:

[selector] {
  width: 200px !important;
}

Solution 1:

div.abc.xyz {
    /* rules go here */
}

... or simply:

.abc.xyz {
    /* rules go here */
}

Solution 2:

Below applies to all tags with the following two classes

.abc.xyz {  
  width: 200px !important;
}

applies to div tags with the following two classes

div.abc.xyz {  
  width: 200px !important;
}

If you wanted to modify this using jQuery

$(document).ready(function() {
  $("div.abc.xyz").width("200px");
});

Solution 3:

If you need a progmatic solution this should work in jQuery:

$(".abc.xyz").css("width", 200);