With a structure like:
<div class="post">
<!-- other divs -->
<div class="post-footer"><!-- footer content here --></div>
</div>
You need to use something like:
.post-footer { display:none; }
.post:hover .post-footer { display: block; }
Alternatively, if you want to make it look smooth, you could use transitions on max-height
:
.post-footer { max-height: 0; transition: max-height 1s linear; }
.post:hover .post-footer { max-height: 300px; /* some value that will always be larger than the height of your footer */ }
Note: browser compatibility table for transitions
Demo for both methods: http://dabblet.com/gist/2819975