//Specify affected tags. Add or remove from list: 
var tgs = new Array( 'div'); 

//Specify spectrum of different font sizes: 
var szs = new Array( 'xx-small','x-small','small','medium','large','x-large','xx-large' ); 
var startSz = 0; 

function ts( trgt,inc ) { 
if (!document.getElementById) return 
var d = document,cEl = null,sz = startSz,i,j,cTags; 

sz += inc; 
if ( sz < 0 ) sz = 0; 
if ( sz > 6 ) sz = 6; 
startSz = sz; 

if (!( cEl = d.getElementById( trgt ) ) ) cEl = d.getElementsByTagName( trgt )[ 0 ]; 

cEl.style.fontSize = szs[ sz ]; 

for ( i = 0 ; i < tgs.length ; i++ ) { 
cTags = cEl.getElementsByTagName( tgs[ i ] ); 
for ( j = 0 ; j < cTags.length ; j++ ) cTags[ j ].style.fontSize = szs[ sz ]; 
} 
}