Checkbox size smaller on FF and Edge

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.3.1/js/bootstrap.min.js"></script>
<div class="roi">
  <div class="form-group">
    <label title="test 1" class="control-label col-sm-10 roi-label">I am the caption 1</label>
    <div class="col-sm-2">
      <input type="checkbox" roiname="roiinput" name="locations" value="1" class="roicheckox form-control FormChoice__Input FormChoice__Input--Checkbox" checked data-f-datainput />
    </div>

    <label title="test 2" class="control-label col-sm-10 roi-label">I am the caption 2</label>
    <div class="col-sm-2">
      <input type="checkbox" roiname="roiinput" name="locations" value="2" class="roicheckox form-control FormChoice__Input FormChoice__Input--Checkbox" unchecked data-f-datainput />
    </div>
  </div>
</div>

CSS

h5.roi-h5 {
  color: #ffffff;
  background-color: #999999;
  padding: 10px !important;
  text-align: center;
  font-size: 20px;
  clear: both;
  margin-top: 20px;
  margin-bottom: 20px;
}

.roi .roidivider {
  height: 30px;
  border-top: solid 1px #999999;
  margin-top: 20px;
}

.roi .roilocations {
  margin-bottom: 20px;
}

.roi-label {
  background-color: #f2f2f2;
  padding: 11px;
  color: #999999;
  display: inline-block;
  vertical-align: middle;
}

.roi label {
  color: #999999;
}

.roi .form-group {
  height: 40px;
  clear: both;
}

.roi .roiinfobox {
  clear: both;
}

.roi input[type='number'] {
  text-align: center;
  color: #db291d;
}

.roi .summary {
  display: none;
}

input.roisavings {
  height: 200px;
  border: 0px !important;
  background-color: #f2f2f2;
  color: #5f96aa;
  font-weight: bold;
  font-size: 35px;
  text-align: center;
}

.roi .roifirstname input,
.roi .roilastname input,
.roi .roicompany input,
.roi .roiemail input {
  border: 0px !important;
  background-color: #f2f2f2;
}

.roi ::placeholder {
  /* Chrome, Firefox, Opera, Safari 10.1+ */
  color: #666F8F;
  opacity: 1;
  /* Firefox */
}

.roi :-ms-input-placeholder {
  /* Internet Explorer 10-11 */
  color: #666F8F;
}

.roi ::-ms-input-placeholder {
  /* Microsoft Edge */
  color: #666F8F;
}

.roi .form-control {
  border: 1px solid #999999;
}

.roi input[type="checkbox"] {
  cursor: pointer;
  -webkit-appearance: none;
  appearance: none;
  background: #fff;
  position: relative;
  width: 40px;
  height: 40px;
  margin-right: auto;
  margin-left: auto;
  border: 1px solid #999999;
}

.roi input[type="checkbox"]:checked {
  background-color: #ffffff;
  content: "+";
}

.roi input[type="checkbox"]:checked:after {
  background: url(https://svgshare.com/i/DMS.svg) no-repeat center center;
  content: '';
  left: 5px;
  height: 28px;
  width: 28px;
  position: absolute;
  top: 2px;
  -webkit-transition: .2s opacity;
  -o-transition: .2s opacity;
  transition: .2s opacity;
}

.roi...