box-sizing

#example1 {
  box-sizing: border-box;
}

* {
  box-sizing: border-box;
}

example1 {
  box-sizing: border-box;
}

*{
 box-sizing: border-box;
 }

header, ul, nav, li, a /* other elements */{

 display: block;
   -webkit-box-sizing: border-box;
   -moz-box-sizing: border-box;
   box-sizing: border-box;

// Defines how the width and height of an element
// are calculated: should they include padding and borders, or not
* {
  box-sizing: border-box;
}