* {
  box-sizing: border-box;
}

$malibu: #59ADEB;
$curious-blue: #193549;

html, body {
  background-color: $malibu;
  color: #fff;
  text-align: center;
}

.checkbox {
  display: inline-block;
  margin-top: 10%;
  padding-left: 1.5rem;
  position: relative;
  transform: translateZ(0);
}

input[type="checkbox"] {
  -webkit-appearance: none;
     -moz-appearance: none;
  
  background: none;
  border: 2px solid #fff;
  border-radius: 0;
  height: 1.125rem;
  left: 0;
  position: absolute;
  top: 0;
  width: 1.125rem;
  
  &:focus {
    border-color: $curious-blue;
    outline: 0;
  }
  
  &.checkmark {
    animation: checkmark-shrink 0.14s ease-out forwards;
    border-width: 0 2px 2px 0;
    transform: rotate(45deg);
  }
  
  &.box {
    animation: box-expand 0.14s ease-out forwards;
  }
  
  &:checked {
    border-color: $curious-blue;
    border-width: 0 2px 2px 0;
    left: 6px;
    height: 1.3125rem;
    transform: rotate(45deg);
    top: -4px;
    width: 0.625rem;
    
    &.box {
      animation: box-shrink 0.14s ease-out forwards;
      border: 2px solid;
    }
    
    &.checkmark {
      animation: checkmark-expand 0.14s ease-out forwards;
      border-width: 0 2px 2px 0;
    }
  }
}

@keyframes box-shrink {
  0% {
    transform: rotate(0deg);
    top: 0px;
    left: 0px;
    width: 18px;
    height: 18px;
  }
  100% {
    transform: rotate(45deg);
    top: 13px;
    left: 5px;
    width: 4px;
    height: 4px;
  }
}

@keyframes checkmark-expand {
  0% {
    transform: rotate(45deg);
    top: 13px;
    left: 5px;
    width: 4px;
    height: 4px;
  }
  100% {
    transform: rotate(45deg);
    top: -4px;
    left: 6px; 
    width: 10px;
    height: 21px;
    border-right-width: 2px;
    border-bottom-width: 2px;
  }
}

@keyframes checkmark-shrink {
  0% {
    top: -4px;
    left: 6px; 
    width: 10px;
    height: 21px;
    border-right-width: 2px;
    border-bottom-width: 2px;
  }
  100% {
    top: 13px;
    left: 5px;
    width: 4px;
    height: 4px;
  }
}

@keyframes box-expand {
  0% {
    transform: rotate(45deg);
    top: 13px;
    left: 5px;
    width: 4px;
    height: 4px;
  }
  100% {
    transform: rotate(0deg);
    top: 0px;
    left: 0px;
    width: 18px;
    height: 18px;
  }
}