When creating an external CSS(Cascading Style Sheet) it is advisable to stick to the following rules:
You may, or may not be aware that it is possible to have “links” to several style sheets. It is sensible to take advantage of this and use filenames for different divisions or classes.
The filename should end with a .CSS extension.
If your website is hosted on a Linux server, please bear in mind that Linux filenames are case sensitive, so it is advisable to stick to only using lowercase.
Avoid using special characters and spaces in CSS filenames. Only use charaters a-z, number 0-9 and use underscore (_), or hyphens (-) in places of spaces.
Always check how your web pages will look in other version of Internet Explorer (IE). If you need to make a CSS change that is only applicable to a specific browser version, use a conditional comment (see below) in your HTML source. Please remember that this is only applicable to Microsoft’s IE and cannot be used with other browsers link Firefox.
<!--[if IE 7]>
<style type="text/css">
body {background-image:url('bgdesert.jpg')}
</style>
<![endif]-->
