Div tags are the basic page layout element we are going to use to design our Web site. Each div can be given a unique identifying code, so that it can easily be controlled by a CSS rule. When using ID to control divs, you should remember that only one div with a given ID should appear on each page. If you already have a div “#container” on a page, do not add another div with the same ID.
Selectors for divs with an ID are written beginning with a pound sign: #
#container
Once a div has a rule defining it’s size, placement, color, etc, additional layout elements can be placed inside the div – much like a picture or text box in InDesign.
A good rule of thumb when using divs is to minimize the number of divs used on the page. Order the divs in a logical manner (such as header, then navigation, then content, then footer) and then use CSS rules to control their placement and appearance.