How do I get rid of an element's offset using CSS?

I've got a positioning problem with some elements, upon inspecting it IE8 Developer tools it shows me this:

Now I'm pretty sure my problem is that 12 offset, but how do I remove it? I can't find any mention of a CSS offset property. Do we need an Offset in addition to margin?

Here is the code thats producing this:

 <div id="wahoo" style="border: solid 1px black; height:100px;">

    <asp:TextBox ID="inputBox" runat="server" />

    <input id="btnDropDown" type="button" style="width:26px; height:26px; background-position: center center; border-left-color: buttonface; background-image: url(Images/WebResource.gif); border-bottom-color: buttonface; border-top-color: buttonface; background-repeat: no-repeat; border-right-color: buttonface;"  tabindex="99" />

    <div id="ListboxWrapper" style="display:none; position:absolute; onfocusout="this.style.display = 'none'"">
       <asp:ListBox ID="lstBoxCompany" runat="server" AutoPostBack="True" OnSelectedIndexChanged="lstBoxCompany_SelectedIndexChanged" style="z-index: 100;" Width="300px" />               
    </div>

</div>

The element with the offset is inputBox