Example :

<div id="... zone-bottom">
<div id="... zone-bottom-item.." class="first">
...
</div>
<div id="... zone-bottom-item.." class="even">
...
</div>
<div id="... zone-bottom-item.." class="last">
...
</div>
....
</div>

It would be interesting to override it in the project to add additional classes. Example : "third".