This happens a lot when porting over CSS-styled HTML markup to ASP.NET, especially when using IDs as CSS selectors (which, as you probably already know, is the "proper" way of doing it).
It has to do with how ASP.NET renames server control IDs that are inside other server controls...
Check your source, and see if where you expect to see ID="Logo" , you see ID="ctl00_Logo" or something like that instead. That would happen if your element with ID="Logo" is inside another control that uses runat="server".
If this happens, your CSS won't work, because it never finds an element with ID="Logo" .
What you have to do to solve this is to:
a) use class selectors instead (bad idea, in my opinion)
b) rename the selector in the CSS stylesheet to ctl00_Logo, or whatever the name in the source is that you are targeting. If you do this, keep in mind that if you end up redesigning the page and creating more server control containers, you may have to adjust your CSS again.
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