Custom checkbox : add cross icon on uncheck using css?

I've been searching a while here and there and can't seem to find a way to stylize the uncheck state of a checkbox. I can change the background to red, but I need to add a cross as well, is it possible in css?

Here is my code and thanks for any help

<label class="customcheck">
  <input type="checkbox" checked="checked">
  <span class="checkmark"></span>
</label>

/* The customcheck */
.customcheck {
  display: block;
  position: relative;
  padding-left: 35px;
  margin-bottom: 12px;
  cursor: pointer;
  font-size: 22px;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
  right: 10px;
}

/* Hide the browser's default checkbox */
.customcheck input {
  position: absolute;
  opacity: 0;
  cursor: pointer;
}

/* Create a custom checkbox */
.checkmark {
  position: absolute;
  top: 0;
  left: 0;
  height: 25px;
  width: 25px;
  background-color: red;
  border-radius: 5px;
}

/* On mouse-over, add a grey background color */
.customcheck:hover input~.checkmark {
  background-color: #ccc;
}

/* When the checkbox is checked, add a blue background */
.customcheck input:checked~.checkmark {
  background-color: #02cf32;
  border-radius: 5px;
}

/* Create the checkmark/indicator (hidden when not checked) */
.checkmark:after {
  content: "";
  position: absolute;
  display: none;
}

/* Show the checkmark when checked */
.customcheck input:checked~.checkmark:after {
  display: block;
}

/* Style the checkmark/indicator */
.customcheck .checkmark:after {
  left: 9px;
  top: 5px;
  width: 5px;
  height: 10px;
  border: solid white;
  border-width: 0 3px 3px 0;
  -webkit-transform: rotate(45deg);
  -ms-transform: rotate(45deg);
  transform: rotate(45deg);
}

input[type=checkbox] {
  position: relative;
}