html {
  background-image: url("../images/brain.jpg");
  background-repeat: no-repeat;
  background-size: 100%;
}

html,
body {
  display: flex;
  width: 100%;
  min-height: 100%;
  justify-content: center;
  align-items: center;
  flex-direction: column;
  font-family: sans-serif;
}

.grid {
  display: grid;
  grid-template-columns: 33% 33% 33%;
  grid-gap: 1%;
  margin-bottom: 1em;
}

h2 {
  color: #777;
}

h4 {
  color: #999;
}

.tgl {
  display: none;
}

.tgl,
.tgl:after,
.tgl:before,
.tgl *,
.tgl *:after,
.tgl *:before,
.tgl+.tgl-btn {
  box-sizing: border-box;
}

.tgl::selection,
.tgl:after::selection,
.tgl:before::selection,
.tgl *::selection,
.tgl *:after::selection,
.tgl *:before::selection,
.tgl+.tgl-btn::selection {
  background: none;
}

.tgl+.tgl-btn {
  outline: 0;
  display: block;
  width: 8em;
  height: 2.3em;
  position: relative;
  cursor: pointer;
  user-select: none;
}

.tgl+.tgl-btn:after,
.tgl+.tgl-btn:before {
  position: relative;
  display: block;
  content: "";
  width: 50%;
  height: 95%;
}

.tgl+.tgl-btn:after {
  left: 0;
}

.tgl+.tgl-btn:before {
  display: none;
}

.tgl:checked+.tgl-btn:after {
  left: 50%;
}

.tgl-flip+.tgl-btn {
  padding: 2px;
  transition: all .2s ease;
  font-family: sans-serif;
  perspective: 100px;
}

.tgl-flip+.tgl-btn:after,
.tgl-flip+.tgl-btn:before {
  display: inline-block;
  transition: all .4s ease;
  width: 100%;
  text-align: center;
  position: absolute;
  line-height: 2em;
  font-weight: bold;
  color: #fff;
  position: absolute;
  top: 0;
  left: 0;
  backface-visibility: hidden;
  border-radius: 4px;
}

.tgl-flip+.tgl-btn:after {
  content: attr(data-tg-off);
  background: #888888;
  -webkit-transform: rotateY(-180deg);
  transform: rotateY(-180deg);
  color: #CCCCCC;
  z-index: -99;
}

.tgl-flip+.tgl-btn:before {
  background: #707070;
  content: attr(data-tg-off);
  color: #FFFFFF;
}

.tgl-flip+.tgl-btn:active:before {
  -webkit-transform: rotateY(-20deg);
  transform: rotateY(-20deg);
}

.tgl-flip:checked+.tgl-btn:before {
  -webkit-transform: rotateY(180deg);
  transform: rotateY(180deg);
}

.tgl-flip:checked+.tgl-btn:after {
  -webkit-transform: rotateY(0);
  transform: rotateY(0);
  left: 0;
  background: #333333;
}

.tgl-flip:checked+.tgl-btn:active:after {
  -webkit-transform: rotateY(20deg);
  transform: rotateY(20deg);
}