CSS Layout with Pixel And Percents

I have a div which contains two nested divs, one that specifies a height of 65 pixels (header), the other which specifies the height as 100% (content) and it is supposed to take the rest of the space veritically. When the page renders, there is a scrollbar on the right because of the height specified of 65 pixels of the header.

What am I doing wrong mixing percents and pixels? I must be missing something. How do I fix this so the content section uses the rest of the page space and I do not have a scroll bar?

Here is the ASP .NET markup and CSS I am using:

<div>
    <asp:ScriptManager ID="ScriptManager1" runat="server"/>
    <div id="header">
        <div style="float: left; height: 100%"><img align="top" alt="" src="~/images/Logo.gif" runat="server"/></div>
        <div style="float: right; height: 100%">
            <div id="outer">
                <div id="middle">
                    <div id="inner">
                        <asp:Label runat="server" ID="ApplicationName" Text="Application" CssClass="appname"></asp:Label>
                    </div>
                </div>
            </div>
        </div>
    </div>

    <div id="content">
        <ig:WebSplitter ID="WebSplitter1" runat="server" Height="100%" Width="100%" 
            DynamicResize="True" CssClass="junk">
            <panes>
                <ig:SplitterPane ToolTip="Navigation Pane" runat="server" Size="20%" CollapsedDirection="PreviousPane" Locked="true">
                    <Template>
                        <asp:ContentPlaceHolder ID="NavigationPlaceHolder" runat="server">
                            <ig:WebDataTree ID="NavTree" runat="server" EnableHotTracking="true" 
                                Height="100%" OnNodeClick="NavTree_NodeClick" SelectionType="Single" 
                                InitialExpandDepth="1"
                                Width="100%" BorderWidth = "0px"
                                EnableAjax ="true">
                                <AutoPostBackFlags NodeClick="On" NodeCollapsed="Off" NodeExpanded="Off" NodeEditingTextChanged="Off" />
                            </ig:WebDataTree>
                        </asp:ContentPlaceHolder>
                    </Template>
                </ig:SplitterPane>
                <ig:SplitterPane Tooltip="Content Pane" runat="server" Size="80%">
                    <Template>
                        <asp:ContentPlaceHolder ID="SiteContentPlaceHolder" runat="server"/>
                    </Template>
                </ig:SplitterPane>
            </panes>
        </ig:WebSplitter>
    </div>
</div>   

html
{
    padding: 0px;
    margin: 0px;
    border: none;
    width: 100%;
    height: 100%;
    font-family: verdana;
    font-size: x-small;
    font-weight: normal;
    font-style: normal;
    font-variant: normal;
    text-transform: none;
    text-transform: none;    
    float: none;       
} 

body
{
    border: none;
    padding: 0px;
    height: 100%;
    width: 100%;
    border: none;
    margin: 0px;
}

form 
{
    border: none;
    margin: 0px; 
    padding: 0px; 
    border: none; 
    height: 100%; 
    width: 100%;
}

span.appname
{
    text-align: right;
    font-family: Arial, Helvetica, sans-serif;
    font-size: 18pt;
    font-weight: bold;
    font-style: normal;
    color: #FFFFFF;
    padding-right: 10px;
}

#header 
{
    background: #295984;
    width: 100%;
    height: 65px;
    overflow: hidden;
}

#content
{
    display: inline;
    width: 100%;
    height: 100%;
}

#outer {height: 100%; overflow: hidden; position: relative; width: 100%;}
#outer[id] {display: table; position: static;}

#middle {position: absolute; top: 50%; width: 100%; text-align: center;} /* for explorer only*/
#middle[id] {display: table-cell; vertical-align: middle; position: static;}

#inner {position: relative; top: -50%; text-align: right;} /* for explorer only */
#inner {width: 100%; margin-left: auto; margin-right: auto;} /* for all browsers*/
#inner[id] {position: static;}