I have a parent class  .parent-class and I wanna apply some style on its only in the case if this class have a child class named as child-class. I did this way and it didn't work:
.parent-class:has(.child-class){
  background: red;  
}
I have a parent class  .parent-class and I wanna apply some style on its only in the case if this class have a child class named as child-class. I did this way and it didn't work:
.parent-class:has(.child-class){
  background: red;  
}
 
    
    As far as I know, there is no way to do this using CSS.
I suggest using jQuery :has() like below. 
$(".box1:has(.box2)").addClass("box3");.box1 {
  width: 100px;
  height: 100px;
  background-color: red;
}
.box3 {
  background-color: yellow;
}<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="box1">
  <div class="box2"></div>
</div>
<div class="box1"></div>