id sector:- select specific element( use only one or two time ).

it is written with in hash character (#). it is unique element.

class sector :- when you want to change group of element.

it is used with a period charecter'.'(full stop symbol) .

should not start with number.

GROUP SECTOR :- used to select all the elments with the same style.

used to minimize the code .

used to separate each selector in grouping .