html, body {
  height: 100%;
  width: 100%;
}

.flex-container {
  
  display: flex;
  
  
  flex-flow: row wrap;
  
  
  justify-content: space-around;
  
  padding: 0;
  margin: 0;
  list-style: none;
}

.flex-item1 {
  background: navy;
  padding: 5px;
  width: 250px;
  height: 150px;
  margin-top: 10px;
  line-height: 150px;
}

.flex-item2 {
  background: red;
  padding: 5px;
  width: 250px;
  height: 150px;
  margin-top: 10px;
  line-height: 150px;
}

.flex-item3 {
  background: gold;
  padding: 5px;
  width: 250px;
  height: 150px;
  margin-top: 10px;
  line-height: 150px;
}

.flex-item4 {
  background: black;
  padding: 5px;
  width: 250px;
  height: 150px;
  margin-top: 10px;
  line-height: 150px;
}