button,
input[type="button"],
input[type="reset"],
input[type="submit"],
.button {
    background-color: #333;
    border: none;
    color: #fff;
    cursor: pointer;
    font-size: 16px;
    font-weight: 300;
    padding: 16px 24px;
    text-transform: uppercase;
    width: auto;
}

button:hover,
input:hover[type="button"],
input:hover[type="reset"],
input:hover[type="submit"],
.button:hover {
    background-color: #e5554e;
    color: #fff;
}

jQuery('form').submit(function() {
    // when form is submitted for the first time change button text
    // and prevent further form submissions
    if (jQuery('form input[type="submit"]').data('submitted') == '1') {
        return false;
    } else {
        // I've also added a class and changed the value to make it obvious to the user that the form is submitting
        // but this is entirely optional and you can customise this as you wish
        jQuery('form input[type="submit"]').attr('data-submitted', '1').addClass('submitting fa fa-spinner fa-spin').val("Submitting");
    }
});