<h1>Find the Kitten! (A Pure CSS Game)</h1>

<div class="container">
  <div tabindex=1></div>
  <div tabindex=2></div>
  <div tabindex=3></div>
  <div tabindex=4></div>
  <div tabindex=5></div>
  <div tabindex=6></div>
  <div tabindex=7></div>
  <div tabindex=8></div>
  <div tabindex=9></div>
  <div tabindex=10></div>
  <div tabindex=11></div>
  <div tabindex=12></div>
  <div tabindex=13></div>
  <div tabindex=14></div>
  <div tabindex=15></div>
  <div tabindex=16></div>
  <div tabindex=17></div>
  <div tabindex=18></div>
  <div tabindex=19></div>
  <div tabindex=20></div>
  <div tabindex=21></div>
  <div tabindex=22></div>
  <div tabindex=23></div>
  <div tabindex=24></div>
</div>

* {
  transition: all .3s linear;
  box-sizing: border-box;
}

h1 {
  font-family: Georgia, sans-serif;
  font-size: 44px;
  font-weight: normal;
  text-align: center;
  margin: 10px 0;
  font-style: italic;
  color: #444;
}

.container {
  overflow: hidden;
  text-align: center;
}

.container div {
  width: 150px;
  height: 150px;
  margin: 10px;
  background: goldenrod;
  cursor: pointer;
  display: inline-block;
}

:nth-child(1):focus {
  outline: none;
  background: url(https://placedog.net/151/151/);
}

:nth-child(2):focus {
  outline: none;
  background: url(https://placedog.net/152/152/);
}

:nth-child(3):focus {
  outline: none;
  background: url(https://placedog.net/153/153/);
}

:nth-child(4):focus {
  outline: none;
  background: url(https://placedog.net/154/154/);
}

:nth-child(5):focus {
  outline: none;
  background: url(https://placedog.net/155/155/);
}

:nth-child(6):focus {
  outline: none;
  background: url(https://placedog.net/150/150/);
}

:nth-child(7):focus {
  outline: none;
  background: url(https://placedog.net/156/156/);
}

:nth-child(8):focus {
  outline: none;
  background: url(https://placedog.net/157/157/);
}

:nth-child(9):focus {
  outline: none;
  background: url(https://placedog.net/158/158/);
}

:nth-child(10):focus {
  outline: none;
  background: url(https://placedog.net/150/150/);
}

:nth-child(11):focus {
  outline: none;
  background: url(https://placedog.net/159/159/);
}

:nth-child(12):focus {
  outline: none;
  background: url(https://placekitten.com/g/150/150);
}

:nth-child(13):focus {
  outline: none;
  background: url(https://placedog.net/160/160/);
}

:nth-child(14):focus {
  outline: none;
  background: url(https://placedog.net/161/161/);
}

:nth-child(15):focus {
  outline: none;
  background: url(https://placedog.net/162/162/);
}

:nth-child(16):focus {
  outline: none;
  background: url(https://placedog.net/163/163/);
}

:nth-child(17):focus {
  outline: none;
  background: url(https://placedog.net/164/164/);
}

:nth-child(18):focus {
  outline: none;
  background: url(https://placedog.net/165/165/);
}

:nth-child(19):focus {
  outline: none;
  background: url(https://placedog.net/166/166/);
}

:nth-child(20):focus {
  outline: none;
  background: url(https://placedog.net/167/167/);
}

:nth-child(21):focus {
  outline: none;
  background: url(https://placedog.net/168/168/);
}

:nth-child(22):focus {
  outline: none;
  background: url(https://placedog.net/169/169/);
}

:nth-child(23):focus {
  outline: none;
  background: url(https://placedog.net/170/170/);
}

:nth-child(24):focus {
  outline: none;
  background: url(https://placedog.net/171/171/);
}

/*************************

Pure CSS "find game" using tabindex and :focus

See:

http://www.impressivewebs.com/using-tabindex-with-focus/

**************************/