Checkbox Error Border

Where in the form do you use the wpcf7-checkbox-not-valid class?

The checkboxes are set up as required. I have this written as css code in my site. This is the code

/* Form Errors */
span .wpcf7-not-valid {
border: 2px solid #CE0000 !important;
}

span .wpcf7-checkbox-not-valid
{
border: 2px solid #CE0000 !important;
}

span.wpcf7-not-valid-tip {
display: none !important;
}

div.wpcf7-validation-errors {
background: #ffe2e2;
border: 2px solid #CE0000 !important;
width: 100% !important;;
color: #CE0000 !important;
font-family:’PT Sans’;
font-size: 16px;
}
.wpcf7 form.invalid .wpcf7-response-output, .wpcf7 form.unaccepted .wpcf7-response-output {
border-color: #CE0000;
}
div.wpcf7-response-output {
font-family:’PT Sans’;
font-size: 18px;
background-color:#F0F0F0;
line-height: 22px;
margin-bottom: 2em !important;
margin-top: 2em !important;
padding: 15px!important;
border-radius: 0px;
box-sizing: border-box;
-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
}

This is the form code:

<label>[text* text-145 placeholder “First Name*”]</label>
<label>[text* text-147 placeholder “Last Name*”]</label>
<label>[email* email-584 placeholder “Email*”]</label>
<label>[text* text-200 placeholder “City*”]</label>
<label>[text* text-201 placeholder “State/Region/Country*”]</label>
Please select one:
[checkbox* checkbox-719 use_label_element “I am a student interested in more information” “I am a College or University interested in membership” “I am a Sponsor interested in sponsorship opportunities”]

<label>[textarea* textarea-338 placeholder “How Can We Assist You?”]</label>

[submit “Send”]

The class is used on the three checkboxes. They should become red if one is not checked.

Where does the idea come from? In reality no wpcf7-checkbox-not-valid class is used anywhere in the form.

OK. Since they were required, I thought they could have a red “error” border same as when a required text field is left blank. Thank you.