I ave a header with a background image and a page container in the body of my page

The HTML:

```
<header>
<nav>Item1-Item2</nav>
</header>

<div class="container">
Content
</div>

```

The css:

```
header{
background: url(images/header.jpg) no-repeat;
background-size: 100% 110%;
position: relative;
z-index: 99999;
}

```

I would liek to set the content of the container to be under the header, so the the header and it's background image overlaps over the top of the page container.

The code above doesn't work, the container seems to be behind but, the background image does not overlap and show over the content area top.

How can I fix this?