HTML 5 Master Page

A master page have a single a html file (.aspx). But the master page can hold any number of user defined controls or you can have multiple nested master pages.
It really depends on what you are trying to do.

I stumbled upon a template created using html 5 and css3 and was wondering if it could be used as a master page

Of course... An aspx master page is not dependent on any specific HTML/CSS version. Open your master page and modify the <DOCYTPE> declaration as well as any other specific HTML5 element that you need to include, and also include your common external stylesheets as well.

Use/Create addtional content areas as needed so that the other aspx pages that will use this master page as their template.

@JorgeM
So for asp.net MVC4 we can use any page for a master page as long as it's named correctly? Or are you saying that we take the default master page and add additional content areas then add our own 'master pages' to those content area's.

I'm new to asp.net and the concept of a master page is a bit confusing - it seems much like a CSS file - but it's not.

Master pages has nothing to do with CSS nor it behave like such.

Please read the folling pages to understand how a master page works:

http://www.codeproject.com/Articles/333650/Beginner-s-Tutorial-on-Master-Pages-in-ASP-NET

http://msdn.microsoft.com/en-us/library/wtxbf3hh(v=vs.100).aspx

@java.beansbureo- yes, master pages can be nested within other master pages.

@AlwMonteiro & JorgeM

Thanks!