Attribute for <STYLE ...>
TYPE

TYPE indicates which style language is being used. TYPE is required, though admittedly virtually all browsers are happy enough without it.

The only really popular style language is W³C's Cascading Styles Sheets. Assuming that's the language you want to use, your <STYLE ...> tag should look like this:

<STYLE TYPE="text/css">

The only other style language with any significant distribution is Netscape's Javascript Style Sheet, supported by Netscape 4. For information on JSSS see Chuck Musciano's excitedly titled The dynamic, powerful abilities of JavaScript Style Sheet.