input[type=checkbox] {
    appearance: none;
    width: 40px;
    height: 40px;
    background-image: url(../img/icon_none.png);
    cursor: pointer;
  }
  
  input[type="checkbox"]:checked::after {
    position: absolute;
    content: url(../img/icon_completed.png);
  }
  
  input[type="checkbox"]:indeterminate::after {
    position: absolute;
    content: url(../img/icon_started.png);
  }
  
  label {
    position: relative;
    bottom: 15px;
  }