Learning my way thru ASP.Net 4 basic web app

I am trying to learn asp.net 4 web app but playing around the web page template shipped in VS 2010.

I clicked New Project --> (Web) ASP.Net Web Application

I click ok.

So now I am trying to manipulate the color of the blue header and the font color or the header text. But I am cant do it thru the css.

Any ideas what is going on in the background?

UPDATE

This is what I get in design time:

This is what I get at r开发者_JAVA百科untime:

If your changes aren't being reflected, try:

• Ctrl-F5
• Perhaps clear your browser cache?
• Try another browser
• If Internet Explorer, ensure your browser is checking for new versions 'Every time I visit the web page'
• Publishing to a new IIS directory, rather than Visual Studio's built in web server.
• Ensure there aren't any caching directives.