How to remove 'quantity' from Marketpress cart


I've built a store that only contains digital products so I need to hide the quantity input box from the checkout. I'm sure this is an easy fix with css but I'm going round in circles to achieve it!

I want to hide the following input type="text":

<td class="mp_cart_col_quant">
<input type="text" size="2" name="quant[3:145:0]" value="1">

I have tried:

.product-details .mp_quantity { display:none; }
.mp_product .mp_quantity { display:none; }
span.mp_quantity { display: none; }

I don't want:
.mp_cart_col_quant { display:none !important; }

Any hints would be great.