Header with color gradient

Hallo

i have a question.

Is it possible to give the header and the footer a color gradient?

I try this code and it works but its not the main header.
#Header { background:linear-gradient(to left, navy, green)}

Here is a picture of the area i mean: http://s0.dealhero24.de/header/

And i have another question.

Have you a list with all selectors or where can I find it?

Sincerely,
Max