[DotNetDevelopment] Where does Class="scrollContainer" come from?

[stapes]

I have the following code in my project (ASP.NET C# Web app):

 <div    id="scroll"
                class="scrollContainer"
                runat="server"
                style="overflow:auto; width:1000px; padding-left:5px
">

I cannot find the class "scrollContainer" defined anywhere in my
project, so where does this class come from. It is working correctly
in most cases, but not on a few. I need to be able to see the
definition and possibly amend it.