How to add the CSS into your Blogger-template
First locate where the CSS should be pasted. Then look for the 'body'-tag in the textarea. Just above the 'body'-tag, add the lines in the next picture.
Almost done - now goto this CSS-link which can be located in the Left-menu of this page. Copy the CSS-text in the textarea, and copy it to the 'marker'-location between the added lines in the picture. Then save your template. Now you are able to copy and use the 'Html/css for blogs'-option when generating Deals and Auctions.
You might also consider searching for another tag: '.post img '. Change the line 'border: 1px solid $bordercolor' to 'border:none' if you don't want a grey border around the center image NSWE.