You can have an absolutely positioned element inside of your relative positioned element:
#container {
position: relative;
}
#background {
position: absolute;
top: 0;
left: 0;
bottom: 0;
right: 0;
z-index: -1;
overflow: hidden;
}
_x000D_
<div id="container">
<div id="background">
Text to have as background
</div>
Normal contents
</div>
_x000D_
Here's an example of it.