Checkbox radius change if checked

This is my css

.round {
  position: relative;
}

.round label {
  background-color: #fff;
  border: 1px solid #ccc;
  border-radius: 50%;
  cursor: pointer;
  height: 28px;
  left: 0;
  position: absolute;
  top: 0;
  width: 28px;
}

.round label:after {
  border: 2px solid #fff;
  border-top: none;
  border-right: none;
  content: "";
  height: 6px;
  left: 7px;
  opacity: 0;
  position: absolute;
  top: 8px;
  transform: rotate(-45deg);
  width: 12px;
}

.round input[type="checkbox"] {
  visibility: hidden;
}

.round input[type="checkbox"]:checked + label {
  background-color: #66bb6a;
  border-color: #66bb6a;
  border-radius:10%;
}

.round input[type="checkbox"]:checked + label:after {
  opacity: 1;
}

I made the border radius change in css but couldn't figure it how to make it in js. Can someone please help me :) I am new to javascript so please don't judge me but i tried with

var checkbox=document.getElementById('checkbox');
if (checkbox.checked){checkbox.style.borderRadius="10%";
}