add_comment_button should be hidden with initially_hidden css class if can_create_comment permission is false => do not set this css property directly on html element.
input.btn {
color:#050;
font: bold 84% 'trebuchet ms',helvetica,sans-serif;
background-color:#fed;
border: 1px solid;
border-color: #696 #363 #363 #696;
filter:progid:DXImageTransform.Microsoft.Gradient
(GradientType=0,StartColorStr='#ffffffff',EndColorStr='#ffeeddaa');
}