Missing default classes for the Quantity field in the 'Shopping cart form' view

Dear Drupal Commerce Team,

I'm altering the CSS of Drupal Commerce, using the ZEN template sub-theme. I have got an issue with the 'Commerce Shopping Cart' at the level /cart. In the carts table, there are missing classes at <th>Quantity</th> :

<form id="views-form-commerce-cart-form-default" accept-charset="UTF-8" method="post" action="/cart">
<div>
<input type="hidden" value="form-Fi_ckOjKweoMKLTAXa4zgvVp-frL3YlaJdHHx7wqAqI" name="form_build_id">
<input type="hidden" value="jSyjWlIg4grc2PVCEWRQDy8KmOV-HXiLlrAYJH_PN2w" name="form_token">
<input type="hidden" value="views_form_commerce_cart_form_default" name="form_id">
<table class="views-table cols-6">
<thead>
<tr>
<th class="views-field views-field-line-item-title"> Product </th>
<th class="views-field views-field-line-item-label"> SKU </th>
<th> Quantity </th>
<th class="views-field views-field-commerce-unit-price"> Price </th>
<th class="views-field views-field-commerce-total"> Total </th>
<th class="views-field views-field-edit-delete"> Remove </th>
</tr>
</thead>
<tbody>
</table>
<div class="line-item-summary">
<div id="edit-actions" class="form-actions commerce-line-item-actions form-wrapper">
</div>
</form>

The result is that I am not able to reach it via my sub-theme. I prefer sending you a query, as I do not want to dabble with the 'Commerce Core'.
I'm grateful for any assistance in solving the matter.
There's a screenshot image uploaded with this post.

Thank you
Jarl