Div does not show the css

I don't find my problem:

body {
  position: relative;
}
#content {
  position: relative;
}
#overlay {
  position: absolute;
  z-index: 10;
  width: 500px;
  height: 150px;
  top: 215px;
}
#callAction {
  position: absolute;
  z-index: 1;
  display: inline-block;
  padding: 38px 110px;
}

<div id="content">
  <div id="overlay">
    <a id="callAction">Button<a>
        </div>
    </div>

The CSS of the a-tag works, but not the css of the div-tag with the id #overlay. What is the problem here??