CSS IDs

IDs are similar to classes , except once a
specific id has been declared it cannot be
used again within the same (X)HTML file.
I generally use IDs to style the layout
elements of a page that will only be needed

once, whereas I use classes to style text and
such that may be declared multiple times.
The main container for this page is defined by
the following.
<div id=”container”>
Everything within my document is inside this
division.
</div>
I have chosen the id selector for the
“container” division over a class, because I
only need to use it one time within this file.
Then in my CSS file I have the following:
#container{
  width: 80%;
margin: auto;
padding: 20px;
border: 1px solid #666;
background: #ffffff;
}
You will notice that the id selector begins
with a (#) number sign instead of a (.)
period, as the class selector does.