CODE EXAMPLE FOR CSS

checkbox background color css

input[type="checkbox"] {
  -webkit-appearance: none;
  -moz-appearance: none;
  appearance: none;

  /* Styling checkbox */
  width: 16px;
  height: 16px;
  background-color: green;
}

input[type="checkbox"]:checked {
  background-color: blue;
}

<input type="checkbox" />