how to make border box in css code example

Example 1: how do i make a boxin html

This is a rectangle!

Example 2: border-box css

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

Example 3: box sizing border box

*{
 box-sizing: border-box;
 }

Example 4: how to style rule to apply the Border Box model css

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

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