.bg {
  position: relative;
  background: #fff;
  display: flex;
  width: 640px;
  height: 640px;
  flex-wrap: wrap;
  margin: 0 auto;
  border: 1px solid #000;
  outline: 6px solid #9a9a9a; }

.intro-wrap {
  padding: 30px 0;
  width: 640px; }

.cell {
  width: 80px;
  height: 80px; }

.cell::before {
  display: block;
  text-align: center;
  font-size: 20px;
  line-height: 36px; }

.queen {
  position: absolute;
  visibility: hidden;
  left: 0;
  top: 0;
  width: 80px;
  height: 80px;
  font-size: 40px;
  line-height: 80px;
  text-align: center;
  text-shadow: 0 0 10px #000;
  color: #fff; }
  .queen.show {
    visibility: visible; }

.row:nth-child(odd) .cell:nth-child(even), .row:nth-child(even) .cell:nth-child(odd) {
  background: #000; }