put an element in a content box code example
Example 1: border-box css
#example1 {
box-sizing: border-box;
}
Example 2: 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;