Cascading style sheets use “id” or “class”

Question

when styling specific html elements, i tend to always use the class attribute. the css code looks cleaner imo.

why do both exist which one should you use and when ?<

Answer 1

ids

#header
#footer
#sidebar
#menu
#content

classes

.important
.warning
.validationError
.recent
.outOfDate
.inactive
.weekDay
.previous
.next
.first
.last