.Net is a framework. Basically, it's a collection of code classes that you can use to write applications or web sites with.
ASP.Net refers to Active Server Pages or code written that is intended to use a web browser for input and output.
VB.Net is a language. C# and VB.Net have different...
I think you're asking about z-index. If you position a div or image as absolute or relative, you can give it a z-index. Higher index are "higher" off the page. So, you could have an overlay div that covers everything with a z-index of 10 or 100 or whatever and then do your content div on top of...