.ow_chat_mailchat_buttons .ow_attachment_btn span.ow_button span {Added to your line base.css now button changed, thanks!
background-color: #ccc;
background-image: none;
border-color: #aaa}
.ow_chat_mailchat_buttons .ow_attachment_btn span.ow_button input[type="submit"], .ow_chat_mailchat_buttons .ow_attachment_btn span.ow_button input[type="button"] {
color: #000;
line-height: 18px;
text-shadow: none;
text-transform: uppercase}