Add image to "proceed to checkout"-button

I would like to add an image to the "proceed to checkout"-button which is displayed in the file cart of the product view. When I use the "hikashop_cart_input_button" class also other buttons change their style.

Best regards

You need to do like us on our demo website with a CSS selector:
.hikashop_cart_module .hikashop_cart_input_button {
background: url(../images/cart_ok.png) no-repeat;
}