CSS 2.1 - styling navigation links with transparent borders
Styling menu links with transparent borders using on hover
ul {width: 600px; margin: 15% auto; list-style: none; padding: 1em 0; text-align: center; border-top: 1px solid grey; border-bottom: 1px solid grey; }
ul li {display: inline; margin: 0.5em; }
ul li a {display: inline-block; width: 15%;} /*make links equal width - 10% of parent width*/
a:link, a:visited {color:gray; border-style: solid; border-width: 1px; border-color: transparent; }
a:hover {border-color: green;} /*changes border color on hover*/