Specific lay-out for every content-type
Based on the comment of the OP (Niels) I changed my answer:

Each content type page will have a different class (node-type-CONTENTTYPE) associated to the BODY element of your HTML.



So you can add to your CSS file:

body.node-type-mycontenttype1 img { border-color: red; }
body.node-type-mycontenttype2 img { border-color: yellow; }




Original answer:

Wich version of Drupal do you use?

For Drupal 7:

You can use a different template for each node of different content type by creating a template:

/site/all/themes/YOUR THEME/templates/node--CONTENTYPE.tpl.php

You can read on Template Suggestions to know which template you can create.

For the CSS, I suggest you to put everything in your main CSS file and not use a different CSS for each content type.