I got it working somewhat. I changed the code a little.
FROM:
.hikashop_cart_button{
background: url('mywebsite.com/images/addtocart.png') !important;
}
TO
.hikashop_cart_button{
background: url('mywebsite.com/images/addtocart.png') !important; width: 50px !important; height: 50px !important; background-repeat: no-repeat !important;
}
It's working great now but I would like to remove the Add to cart text which I can probably just delete from the language file and I would also like to remove the border around the Add to cart button.
Also, I have it set up so when an item is added to cart, the popup appears and both the Continue Shopping and Proceed to Cart buttons are the same as my add to cart button.