PHP just outputs HTML. CSS is typically a static file on its own. It can be hand-coded, or generated by something like Dreamweaver.
CSS itself isn't so bad.
"Get the body element and set its background to the color #C3D9FF; text color to #000000; font size to 10pt; font family (in order of preference) to verdana, geneva, ... etc; top/right/bottom/left margins to 5/10/10/10 pixels respectively; and padding to 0."
font: 10pt verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif;
margin: 5px 10px 10px 10px;
If you know what you want to achieve, you could just look through a CSS reference.