The following CSS can be used to style and position the submit button on a gravity form field.

Please replace the FORMID with the ID of the gravity form e.g. body #gform_wrapper_2

body #gform_wrapper_FORMID .gform_footer input[type=submit]{
float: right;
margin: 0 50% 0 0;
border-style: solid;
border-width: 2px;
border-color: white !important;
background:#afabab;
color:white;
}