style.css

* {
  box-sizing: border-box;
}

body {
  font-family: "Helvetica Neue", Arial;
  margin: 0;
}

.app {
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  display: flex;
  flex-direction: column;
}

.tips {
  background: #ccc;
  padding: 15px;
}

.viewport {
  position: relative;
  overflow: hidden;
  flex: 1;
}

@keyframes konamiTime {
  0% {background-color: #45CEEF;}
  25% {background-color: #FFF5A5;}
  50% {background-color: #FFD4DA;}
  75% {background-color: #99D2E4;}
  100% {background-color: #D8CAB4;}
}

.viewport.konamiTime {
  animation: konamiTime 2s infinite linear;
}

.node {
  z-index: 5;
  position: absolute;
  background: black;
  color: white;
  display: flex;
  align-items: center;
  justify-content: center;
}

.node:focus {
  background: blue;
}