I'm not able to center an inner, `position: absolute` element inside of an `position: relative` element ( <https://jsfiddle.net/qL0c8cau/> ):

```css
html,body,div {margin:0;padding:0;}
.one {
  position: relative;
  margin: 50px auto;
  width: 200px;
  height: 100px;
  background: #900;
}
.two {
  position: absolute;
  top: 0;
  bottom: 0;
  right: 0;
  left: 0;
  margin: auto;
  background: #0f0;
  opacity: 0.3;
  height: 160px;
  width: 400px;
}
```

```html
<div class="one">

  <div class="two"></div>

</div>
```

I can't see what is wrong with it. I set everything correct, but it's not aligned horizontally for some reason.

What am I doing wrong here?