You can style that button with:
#wa_Show_Checkout .eC_FormButton {
background-color: #b0a091;
border: medium none !important;
color: white;
font-family: Taviraj,Georgia,Times,"Times New Roman",serif;
padding: 0.7em 1.2em;
}
You can change the text on the checkout button from the confirm.php page.
If you give me FTP access I'll look into why it is setting the form height too high. I'll have to debug the javascript that does it.