I have to disagree. Use of the following tags MUST be avoided in a template:
!DOCTYPE...
<html>...</html>
<meta... />
<head>...</head>
<title>...</title>
<style>...</style>
<body>...</body>
Injecting CSS blocks or any of the above in the middle of a page is bad practice. Why? because in CSS blocks, you can define Classes that have the same name as an already declared Class. Doing so, some properties of the original Class may be overwritten which can result in a totally defaced page (by "page" I mean the entire document, not just your ad' section).
I am therefore surprised that eBay tolerates CSS block declarations within the Body of the document and they will change it sooner or later. When they do, you will have to re-write all of your templates. Also, navigators may get tighter on the subject in the future and ignore or disallow CSS block declarations within the Body section.
The only way to write a long-live, eBay-compliant template is to write in-line CSS using <div style="..."> or <span style="...">. This is totally acceptable but the drawback is that it takes for ever to code!
As far as automated (WYSIWYG) eBay template generators are involved, to my knowledge, only http://www.auctiondecorator.com/ does it properly because it generates in-line CSS code only, which makes it fully compatible with eBay rules and regulations.