mlddev on "[Plugin: WooCommerce - excelling eCommerce] CSS - Customization"

For styling the price overlay banner thingy you can achieve that by editing your theme file CSS.

The example site is styling the HTML element:
<span class="price"> on the category page, and not the
<span class="onsale">

Since the "onsale" is already styled in a manner to hover over products with a set sale price, you will need to decide how you want to deal with that, by either hiding that through CSS, or removing it through your theme functions.php.

You can also do 2. with CSS, something like this:

.woocommerce ul.products li.product .price ins, .woocommerce-page ul.products li.product .price ins {
  background: none repeat scroll 0 0 transparent;
  float: left;
  margin-right: 3px;
}