.wpcf7 form.sent .wpcf7-response-output {
    border: none;
    color: green;
    font-weight:bold;
    text-align:center;
}
.wpcf7 form.invalid .wpcf7-response-output, .wpcf7 form.unaccepted .wpcf7-response-output, .wpcf7 form.payment-required .wpcf7-response-output {
    border:none;
    color:#f00;
    font-weight:bold;
    text-align:center;
}
.wpcf7 form .wpcf7-response-output {
    border:none;
}