用不着JavaScript的吧，CSS就有这功能：
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML Strict//EN"><META http-equiv="Content-Type" content="text/html; charset=utf-8"> <!DOCTYPE HTML PUBL
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML Strict//EN"><META http-equiv="Content-Type" content="text/html; charset=utf-8"> <!DOCTYPE HTML PUBL
