如何更改不同子类的弹出窗口宽度？

    <span class="grandparent">
        <span class='parent'>
            <span id="popUP" class="child1">
                Some content for popUP
             </span> <!-- 1st child has width of 390px-->
        </span>    
    </span>
    <span class="grandparent">
        <span cl