This is all CSS:

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• Two
• Three

This page does not use any Javascript. It's better because it preloads itself and works in any browser. Plus, search engines and screen readers see the content of the buttons as text.

Here's what it looks like to robots:

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Here's the CSS:

a,a:hover,a:active,a:visited { outline:0 }
#navigation li {
   list-style:none;
   display:inline;
   margin:0;
   margin-right:5px
}
#navigation li a {
   display:inline-block;
   width:100px;
   height:30px;
   text-indent:100%;
   overflow:hidden;
   background-image:url('buttons.png');
   background-repeat:no-repeat
}
#navigation a#one { background-position:0 0 }
#navigation a#two { background-position:-100px 0 }
#navigation a#three { background-position:-200px 0 }
#navigation a#one:hover { background-position:0 -30px }
#navigation a#two:hover { background-position:-100px -30px }
#navigation a#three:hover { background-position:-200px -30px }
#navigation a#one:active { background-position:0 -60px }
#navigation a#two:active { background-position:-100px -60px }
#navigation a#three:active { background-position:-200px -60px }