html绝对路径，相对路径

.com/eat.php中引用.com/includes/headrt.php的话写includes/header.php

.com/service/eat.php中引用.com/includes/headrt.php的话写../includes/header.php

href="/"表示根目录，从.com/eat.php变到.com/service/eat.php时不用改