通过 CSS 将鼠标悬停在父元素上时显示 :after

Is it possible to display:block; the :after pseudo-element when I hover over the parent element itself?

#myDiv{
   position:relative;
   width:50px;
   height:50px;
   border-style:solid;
   background-color:red;
}
#myDiv:after{
   position:absolute;
   content:"";
   display:none;
   width:50px;
   height:50px;
   border-style:solid;
   background-color:blue;
}

我累了:

#myDiv:hover #myDiv:after{
    display:block;
}
#myDiv:hover + #myDiv:after{
    display:block;
}
#myDiv:hover > #myDiv:after{
    display:block;
}

但运气不好，这里有一个 fiddle.