css - Position on ::after in table-cell doesn't work in Firefox?

Question

The following code should create a pseudo-element which spans 100% of its parent element's width. However this won't work in Firefox, it does work in Chrome. Firefox seems to ignore the .parent's position:relative. Is this a bug?

HTML

<div class="parent">

</div>

CSS

.parent{
  background:red;
  width:100px;
  height:100px;
  position:relative;
  display:table-cell;
}

.parent:after{
left:0;
  content:'';
  right:0;
  top:10px;
  height:20px;
  background:green;
  position:absolute;
}

Live demo

See this images in chrome

and now see this result in firefox

---

Answer 1

如果可能，将 更改display:table-cell为block或inline-block以修复此错误。或者，position:relative将父级更改为absolute.

Answer 2

给width

  .parent:after{
      left:0;
      content:'';
      right:0;
      top:10px;
      width:100px;
      height:20px;
      background:green;
      position:absolute;
}