Can't get inner div to scroll

Can't get inner div to scroll

I'm trying to get a div to scroll but have the page not scroll.
The  div "content" is being replaced by javascript using innerHTML.

I cannot get the content div to scroll with the following code. But it does scroll if I put in height:800px. But I don't want to specify the height because this might be on the desktop or mobile device. I want the height to be by percentage.

I have the following structure

<body>
<div id=header style="height:100%">headerinfo</div>
<div id=content style="height:100%;overflow:auto">content which is replaced dynamically</div>
</body>

Any suggestions?