adding values for checkbox for php mailer

I have a checkbox, I have turned into a male/female slider. Im confused how can I make a value for these in the HTML??? off=male on=female I know I have to somehow turn unchecked into male and checked into female but how do I code this in the html? So when I make a mailer script I can email these values to me?

<span style='font-size: px;'>Gender:$gender<br></span>

.switch {
  position: relative;
  display: inline-block;
  width: 90px;
  height: 34px;
}

.switch input {display:none;}

.slider {
  position: absolute;
  cursor: pointer;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: #0024FF;
  -webkit-transition: .4s;
  transition: .4s;
   border-radius: 34px;
}

.slider:before {
  position: absolute;
  content: "";
  height: 26px;
  width: 26px;
  left: 4px;
  bottom: 4px;
  background-color: white;
  -webkit-transition: .4s;
  transition: .4s;
  border-radius: 50%;
}

input:checked + .slider {
  background-color: #FF1493;
}

input:focus + .slider {
  box-shadow: 0 0 1px #2196F3;
}

input:checked + .slider:before {
  -webkit-transform: translateX(26px);
  -ms-transform: translateX(26px);
  transform: translateX(55px);
}

/*------ ADDED CSS ---------*/
.slider:after
{
 content:'Male';
 color: white;
 display: block;
 position: absolute;
 transform: translate(-50%,-50%);
 top: 50%;
 left: 50%;
 font-size: 10px;
 font-family: Verdana, sans-serif;
}

input:checked + .slider:after
{  
  content:'Female';/*ON*/
}

/*--------- END --------*/

<label class="switch"><input type="checkbox" name="gender" id="togBtn"><div class="slider round"></div></label>

I have a checkbox, I have turned into a male/female slider. Im confused how can I make a value for these in the HTML??? off=male on=female I know I have to somehow turn unchecked into male and checked into female but how do I code this in the html? So when I make a mailer script I can email these values to me?