Replace #my-form-id with the unique id of your form

example.css

#my-form-id input[type=radio] {
  position: absolute; 
  opacity: 0;
  cursor: pointer;  
}

#my-form-id input[type=radio] + .wpcf7-list-item-label:before {
  content: "V";
  display: inline-block;
  padding-right: 5px;
  font-family: 'ETmodules';
  line-height: 1em;
  vertical-align: middle;
}

#my-form-id input[type=radio]:checked + .wpcf7-list-item-label:before {
    content: "Z";
}

/* label color when checked */
#my-form-id input[type=radio]:checked + .wpcf7-list-item-label {
    color: green;
}