父项悬停时如何更改伪元素子项?

我正在尝试获取一个将其作为父元素悬停时要更改的伪元素的项目.这里的伪元素是.child:after.我知道这可行:

I'm trying to get an item that is a pseudo element to change when the parent is hovered over. The pseudo element here is .child:after. I know this works:

.parent:hover .child { 
   background: #FF0000; 
  }

但这似乎不起作用:

.parent:hover .child:after { 
   background: #FF0000; 
  }

有什么想法吗?谢谢！！

Any ideas? Thank you!!