Using Php in your CSS (Cascade Style Sheet) is not "proper",
Also, You can use Php in your HTML:
<body>
<?php if (condition){ ?>
<div id="content">
Foo bar
</div>
<?php } ?>
</body>
With this code, div block don't appear, (and you don't use it with JavaScript), You can use this for just hidden your div :
<body>
<div id="content" <?php if (condition){ echo 'style="display:none;"'; } ?>>
Foo bar
</div>
</body>
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…