.square {
  width: 33px;
  height: 33px;
  background: #eee;
  font-size: 125%;
  line-height:1em;
  text-align:center;
  border: 1px solid #000;

  -webkit-user-select: none;
  -khtml-user-select: none;
  -moz-user-select: none;
  -o-user-select: none;
  user-select: none;
}

td:nth-of-type(3n) {
   border-right: 3px solid blue !important;
}

tr:nth-of-type(3n) td {
   border-bottom: 3px solid blue !important;
}

#sudokuboard {
   border: 3px solid blue !important;
}