外部文件连接：<link rel ="stylesheet" type=""text/css" href="demo.css"/>
内联CSS：<style type="text/css">
a:link img{
filter:gray;
}
a:hover img{
filter:"";
}
</style>
html规范：<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
编码格式：<meta http-equiv="content-type" content="text/html;charset=utf-8"/>
PHP文件乱码：header("Content-type:text/html;charset=utf-8");
json格式化：header("Content-type:text/json;charset=utf-8");