AJAX :: Set MultiHandleSliderExtender Length To A Percent Of Its Container

I'm using a MultiHandleSliderExtender (very cool) and need to set its Length property to a percent of its DIV container. The extender appears to only allow a decimal value for the number of pixels. Can anyone show me how to set the Length to, say, 95% of the DIV? I suppose using javascript to dynamically set it? I'm a C# guy who struggles with javascript and I cannot make this fly on my own.

<div
style="width:100%;
border:solid
thin red">
<asp:TextBox
ID="TextBox1"
runat="server"
Width="500px"></asp:TextBox><br
/><br
/>
<asp:TextBox
ID="TextBox2"
runat="server"
Text="648"
></asp:TextBox><br
/>
<asp:TextBox
ID="TextBox3"
runat="server"
Text="672"
></asp:TextBox><br
/>
<asp:MultiHandleSliderExtender
ID="TextBox1_MultiHandleSliderExtender"
runat="server"
Enabled="True"
HandleAnimationDuration="0.1"
Maximum="672"
Minimum="0"
TargetControlID="TextBox1"
OnClientDragEnd="SliderDragEnd"
OnClientValueChanged="SliderDragEnd"
Length="1200" >
<MultiHandleSliderTargets>
<asp:MultiHandleSliderTarget
ControlID="TextBox2"
/>
<asp:MultiHandleSliderTarget
ControlID="TextBox3"
/>
</MultiHandleSliderTargets>
</asp:MultiHandleSliderExtender>
</div>