Master Pages are more pfor the physical layout of you HTML, more like a template for your pages.
So you would but your table strucutre, headers, and objects in the master page. Then yo page is associated to a master page, and it will take on that wrapper HTML.
CSS - in 2.0 is meant to go inside a theme, app_themes, and themes are more like "clothing" for your app. CSS lets you do things like colors, fonts, positioning, and much more, but it does not actually have an HTML elements in it. It is a definition of style for the HTML elements in yoru page.
You would use CSS to "dress" the html in your master page.
So in yo master you might have something like
<asp:label runat="server" cssclass="myclass" .....
and in your css
.myclass{ color:red; font-size:15px;}
what will happen is when the page renders, it will include the label from the master page, and whatever text in that label, will be assigned the myclass css class which will cause the browser to paint that label red and font size of 15 pixels.
Jonathan Minond
http://www.Jonavi.com
http://www.jonavi.com/Default.aspx?pageID=21
http://RainbowBeta.com
http://community.rainbowportal.net/blogs/jonathans_rainbow_blog/default.aspx
http://dotnetslackers.com/community/blogs/jminond/default.aspx