Apply some css on parent element based on the child element

Question

For eg I have a structure like this

<div class="dialog">
     <div class="child1">
     </div>
</div>
<div class="dialog">
     <div class="child2">
     </div>
</div>
<div class="dialog">
     <div class="child3">
     </div>
</div>

I need to apply some CSS to the parent that contains an element as the class name "child1" please suggest