*,
::after,
::before {
  -webkit-box-sizing: border-box;
          box-sizing: border-box;
  margin: 0;
}

body {
  background-color: #333;
  height: 100%;
}

.back {
  margin: 30px 20px;
}
.back__title {
  font-family: Impact, Haettenschweiler, "Arial Narrow Bold", sans-serif;
  font-size: 30px;
  color: #fff;
  text-decoration: none;
  font-weight: lighter;
  padding: 10px 50px;
  background-color: hsl(20, 25%, var(--text-lightness));
  border-radius: 1vmin;
  -webkit-transition: all 0.2s;
  transition: all 0.2s;
}
.back__title:hover {
  background-color: #fff;
  color: hsl(20, 25%, var(--text-lightness));
}

.container {
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-pack: center;
      -ms-flex-pack: center;
          justify-content: center;
  -webkit-box-align: center;
      -ms-flex-align: center;
          align-items: center;
}

.board {
  --cell-size: 20vmin;
  --cell-gap: 2vmin;
  position: relative;
  display: -ms-grid;
  display: grid;
  -ms-grid-columns: var(--cell-size) var(--cell-gap) var(--cell-size) var(--cell-gap) var(--cell-size) var(--cell-gap) var(--cell-size);
  grid-template-columns: repeat(4, var(--cell-size));
  -ms-grid-rows: var(--cell-size) var(--cell-gap) var(--cell-size) var(--cell-gap) var(--cell-size) var(--cell-gap) var(--cell-size);
  grid-template-rows: repeat(4, var(--cell-size));
  gap: var(--cell-gap);
  border-radius: 1vmin;
}

.board > *:nth-child(1) {
  -ms-grid-row: 1;
  -ms-grid-column: 1;
}

.board > *:nth-child(2) {
  -ms-grid-row: 1;
  -ms-grid-column: 3;
}

.board > *:nth-child(3) {
  -ms-grid-row: 1;
  -ms-grid-column: 5;
}

.board > *:nth-child(4) {
  -ms-grid-row: 1;
  -ms-grid-column: 7;
}

.board > *:nth-child(5) {
  -ms-grid-row: 3;
  -ms-grid-column: 1;
}

.board > *:nth-child(6) {
  -ms-grid-row: 3;
  -ms-grid-column: 3;
}

.board > *:nth-child(7) {
  -ms-grid-row: 3;
  -ms-grid-column: 5;
}

.board > *:nth-child(8) {
  -ms-grid-row: 3;
  -ms-grid-column: 7;
}

.board > *:nth-child(9) {
  -ms-grid-row: 5;
  -ms-grid-column: 1;
}

.board > *:nth-child(10) {
  -ms-grid-row: 5;
  -ms-grid-column: 3;
}

.board > *:nth-child(11) {
  -ms-grid-row: 5;
  -ms-grid-column: 5;
}

.board > *:nth-child(12) {
  -ms-grid-row: 5;
  -ms-grid-column: 7;
}

.board > *:nth-child(13) {
  -ms-grid-row: 7;
  -ms-grid-column: 1;
}

.board > *:nth-child(14) {
  -ms-grid-row: 7;
  -ms-grid-column: 3;
}

.board > *:nth-child(15) {
  -ms-grid-row: 7;
  -ms-grid-column: 5;
}

.board > *:nth-child(16) {
  -ms-grid-row: 7;
  -ms-grid-column: 7;
}
.board__cell {
  background-color: #444;
  border-radius: 1vmin;
}
.board__tile {
  --y: 1;
  --x: 2;
  position: absolute;
  top: calc(var(--y) * (var(--cell-size) + var(--cell-gap)));
  left: calc(var(--x) * (var(--cell-size) + var(--cell-gap)));
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-pack: center;
      -ms-flex-pack: center;
          justify-content: center;
  -webkit-box-align: center;
      -ms-flex-align: center;
          align-items: center;
  width: 20vmin;
  height: 20vmin;
  border-radius: 1vmin;
  font-family: Impact, Haettenschweiler, "Arial Narrow Bold", sans-serif;
  font-size: 7.5vmin;
  font-weight: lighter;
  background-color: hsl(25, 60%, var(--bg-lightness));
  color: hsl(20, 25%, var(--text-lightness));
  -webkit-transition: 100ms;
  transition: 100ms;
  -webkit-animation: show 200ms;
          animation: show 200ms;
}

@-webkit-keyframes show {
  0% {
    opacity: 0.5;
    -webkit-transform: scale(0);
            transform: scale(0);
  }
}

@keyframes show {
  0% {
    opacity: 0.5;
    -webkit-transform: scale(0);
            transform: scale(0);
  }
}