var head=document.getElementsByTagName( "HEAD" );
var new_link = document.createElement( 'link' );
new_link.type = 'text/css';
new_link.href = 'css/style.css';
head[0].appendChild( new_link );
var new_link = document.createElement( 'link' );
new_link.type = 'text/css';
new_link.href = 'css/style.css';
head[0].appendChild( new_link );
var new_link = document.createElement( 'link' );
new_link.type = 'text/css';
new_link.href = 'css/style.css';
new_link.rel="stylesheet"; //还要加上这句才行
head[0].appendChild( new_link );