pop up width smaller with my buttons

Hi,

The fact that you can't see the second button because of the width of the page in the popup comes from the CSS of your template which probably has a min-width set on the body of the popup which it shouldn't.
You can try to add such CSS in the CSS of your template:
body{ min-width : auto !important; }
but we can't tell you if that's the correct code or if it will have side effects since we don't know the CSS of your template.
Normally, joomla templates should apply the min-width attribute only on the normal pages, not in popups.

Regarding the buttons themselves, you can take example on the CSS code on our demo website where we add images on these buttons:
#hikashop_add_to_cart_continue_div .hikashop_cart_input_button {
background-image: url(../images/shopping.png);
background-position: right;
background-repeat: no-repeat;
background-color: transparent;
color: #167e93;
padding-right: 45px;
height: 40px;
font-weight: bold;
}
#hikashop_add_to_cart_checkout_div .hikashop_cart_input_button {
background-image: url(../images/checkout.png);
background-position: right;
background-repeat: no-repeat;
background-color: transparent;
color: #167e93;
padding-right: 45px;
height: 40px;
font-weight: bold;
}