Cut and Pasting Code

I have used one of the Dreaweaver CSS templates and would like to add a second
header immediately below the first (and resize it to fit my needs later).

Not being a pro in code, it seems to me that the simple solution should be to
go into the the Split view (design and code), double-click on the <div#header>,
and copy and paste the hi-lighted code. But nothing happens.

Am I missing something? Am I being stupid (I'm often quite good in that
department)? This is a timely issue, can somebody out there help me?

That would be invalid code if you just copy and paste a div with an ID. IDs in
CSS are unique and if you have more than one ID your page will not validate.
In order to make this work you will need to change the ID "header" to a class
and then change those DIVS to class="header" instead of ID="header". For the
CSS document, the # represents an ID, so change that to a . which defines a
class.

For a good quick tutorial on basic CSS check out the following link:

http://www.w3schools.com/css/

Thank you--will get right on it!