Simple flexbox 2x2 matrix

gistfile1.txt

/* HTML */
<div class="container">
  <div class="tile">1</div>
  <div class="tile">2</div>
  <div class="tile">3</div>
  <div class="tile">4</div>
</div>

/* CSS */
.container {
  display: flex;
  width: 200px; // change based on the need
  height: 200px; // change based on the need
  flex-wrap: wrap;
}
.container .box {
  flex-basis: 50%;
}