When 1 px border is added to div, Div size increases, Don’t want to do that [duplicate]

This is also helpful in this scenario. it allows you to set borders without changing div width

textarea { 
  -webkit-box-sizing: border-box; /* Safari/Chrome, other WebKit */
  -moz-box-sizing: border-box;    /* Firefox, other Gecko */
  box-sizing: border-box;         /* Opera/IE 8+ */
}

Taken from http://css-tricks.com/box-sizing/