.wpcf7-not-valid-tip {
  font-size: 16px;
  background: #000;
  text-align: center;
}
.wpcf7-response-output {
  font-size: 16px !important;
}
.wpcf7 form.sent .wpcf7-response-output {
  text-align: center !important;
}
@media only screen and (max-width: 800px) {
  input#your-name {
    width: 100% !important;
    margin-top: 1em !important;
  }
  input[type="submit"] {
    width: 100% !important;
    margin-top: 1em;
    margin-left: 0px !important;
  }
}