@source https://stackoverflow.com/questions/7600173/specify-csss-for-webkit-ie-without-separate-css
.htaccess
<IfModule mod_setenvif.c>
BrowserMatch "Mozilla" USER_AGENT=firefox
BrowserMatch "Safari" USER_AGENT=safari
BrowserMatch "Chrome" USER_AGENT=chrome
BrowserMatch "MSIE" USER_AGENT=ie
</IfModule>
php
<body class="<?=$_SERVER['USER_AGENT'];?>">