ID

An id is used to uniquely identify an element in the body. Only one element in a page may have a particular id assigned. This will be crucial for CSS positioning techniques as well as for effective Javascripting. If you feel your CSS rule needs to be used on more than one tag, use a .class instead of an #id.

1. define the id in CSS
   #idname { ...css style rules... }
2. apply the id to no more than one element in the body
   <tagname id="idname"></tagname>