When specify more than one class for divCenter  panel  like so:

                    <asp:Panel ID="divLeft" runat="server" CssClass="leftside home" Visible="true">
                        <asp:ContentPlaceHolder ID="leftContent" runat="server" />
                        <portal:PageMenu id="PageMenu1" runat="server" UseTreeView="true" TreeViewShowExpandCollapse="false" />
                    </asp:Panel>
                    <asp:Panel ID="divCenter" runat="server" CssClass="center-rightandleftmargins home" Visible="true">
                        <asp:ContentPlaceHolder ID="mainContent" runat="server" />
                    </asp:Panel>
                    <asp:Panel ID="divRight" runat="server" CssClass="rightside home" Visible="true">
                        <asp:ContentPlaceHolder ID="rightContent" runat="server" />
                    </asp:Panel>

the home class never gets rendered into the output.  I'm doing the same for  divLet and divRight panels and those are fine, but it looks like the code disregards  CssClass attribute for the middle div as it's changed depending on whether there's content  in the side divs or not.

I understand that it changes the class of the center div to one of the four.  However, I have an additional class assigned which I want to stay there.  How come it's gone?

Yes, I understand this is how the 3-column layout works here. It would be nice if the code was a little more intelligent and didn't strip off other classes assigned to the div, that's all.  There is a reason why I'm using "home" class.  I've worked around this because it's not really an issue, but people should be able to set more than one CssClass to the middle div and not have to worry about it being stripped off by the code just because it assigns it based on weather content in left/right column  is present or not.

Yes, I've already been thinking of doing that.  Will explore this option further once break starts.  Thanks Joe!