ya...betul boss...Simple rule: You cannot have reference links in html emails. So your "<link href..." will not work.
Hence all your styles should be inline in the style tag. If you want to be even more safer use them inside your tags but you will have a lot of repetitive coding to do.
That's why lot of e-commerce html is mostly images because html coding is painful and there is no 100% guarantee that they will work in all clients like outlook, gmail, hotmail, yahoo etc. Every mail client reads html emails differently.
Check articles on litmus or mailchimp for tips on html templates.
Welcome to the nasty world of html templates