style.css

body {
  background-color: #ecf0f1;
}

.center {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}
input[type="checkbox"] {
  position: relative;
  width: 80px;
  height: 40px;
  border-radius: 20px;
  background-color: red;
  -webkit-appearance: none;
  outline: none;
}
input:checked[type="checkbox"] {
  background-color: green;
}
input[type="checkbox"]::before {
  position: absolute;
  content: "";
  top: 0;
  left: 0;
  background-color: floralwhite;
  width: 40px;
  height: 40px;
  border-radius: 20px;
  transform: scale(0.8);
  transition: 0.5s;
}
input:checked[type="checkbox"]::before {
  left: 40px;
}