Not working with my tumblr code

[vfluttershy]

Hi and thanks for the code! For some reason the code isn't working with my theme and I was wondering if you had any tips or could help me out. I put the CSS code above < /head> like this:

{CustomCSS}
<style>
   {block:IndexPage} 
    .books {
        display:none;
        }
    {/block:IndexPage}

    {block:TagPage}
    .books {
        display:block;
        }
  {/block:TagPage}
</style>
</head>

But I can't find where to put the {TagsAsClasses} code. I don't have a div id after the {block:Posts}. I have a {block:Date}. I've tried inserting it into all of my div ids, but I'm not having any luck.