div.wpforms-container-full .wpforms-form input[type=submit], 
div.wpforms-container-full .wpforms-form button[type=submit] {
    background-color: #eee; /* Grey background */
    border: 1px solid #ddd; /* Dark grey border */
    color: #333; /* Black text color */
    font-size: 1em; /* Size of text */
    padding: 10px 15px; /* Distance between text and border */
}