why a tag doesn't get parent styles when it is a button?

Question

I observed that button tags don't inherit styles from parent div in Firefox.

Given the following markup:

<div id="post-footer-left">
    <div id="post-edit">
          <div id="edit_article_text">..</div>
    </div>

    <div id="post-delete">
        <form id="delete_article_trigger" action="..." method="post">
             <input type="hidden" name="_method" value="DELETE" />
             <button type="submit">
                  <div id="delete_article_text"></div>
             </button>
        </form>
   </div>

   <div id="post-sold">
         <div id="bought_article_text"></div>
   </div>
</div>

CSS:

#post-footer-left
{
   font-size:10px;
}

Now all the text inside the div#post-footer-left are with font size equal to 10 pixels. except the text inside the button. Thanks for any explanations on this. I know one of the solution is to add more CSS rules for the div inside button, but I am interested to understand the issue first.

Thanks.