<div class="big-wrap">
    <div class="block block-1">1</div>
    <div class="block block-2">2</div>
    <div class="block block-3">3</div>
    <div class="block block-4">4</div>
  </div><!-- big-wrap -->

.big-wrap {
  display: flex;
  flex-flow: row wrap;
  align-content: center;
/* Comment out the next line to see the effect */
  align-items: center;

/* etc. */
  height: 50vh;
  background-color: white;
  padding: 10px;
  border: 1px solid black;
}

.block {
  color: white;
  font-size: 2.6rem;
  text-align: center;
  padding: 10px;
  border: 1px solid black;
  width: 100px;
  height: 100px;
}

.block-1 {
  background-color: #dcf1fe;
  height: 150px;
}

.block-2 {
  background-color: #50bcfa;
  width: 150px;
/* Toggle this to override the align items */
/*   align-self: baseline; */
}

.block-3 {
  background-color: #0379bd;
  height: 150px;
}

.block-4{
  background-color: #fec333;
}