Can't remove the product condition field

[Spym]

I can't remove the product condition field from the default theme of PrestaShop v1.6.0.9.

 

I tried to add the following to /themes/default/css/product.css:

#product_condition{
   display:none;
}

Then cleared the cache as shown here: http://mypresta.eu/en/art/prestashop-16/clear-cache.html

 

The browser's cache was cleared as well, but the field is still there.

 

What I'm missing there? Which additional information I need to provide to get help?

 

Thanks in advance.