Динамичное изменение размера шрифта на сайте

<style>#fontresize {
background:url(mtop1.png) repeat-y;
border:#aaa 1px solid;
color:#505050;
font:bold 12px arial,helvetica,sans-serif;
padding:5px 1px 0;
position:fixed;
top:5px;
left:5px;
text-align:center;
}
*html #fontresize {
position:absolute;
left:10px;
top:expression(eval(document.documentElement.scrollTop) + 5 + 'px')}
#fontresize a {
text-decoration: none;
background:url(mtop.png) repeat-x;
border:#c0c0c0 1px solid;
color:#c0c0c0;
display:block;
font:bold 12px arial,helvetica,sans-serif;
margin:1px 0;
padding:2px;
}
#fontresize a:hover {
text-decoration: none;
border:#505050 1px solid;
color:#505050;}
#fontresize a:active {
text-decoration: none;
border:#505050 1px solid;
color:#505050;}</style>