.flex-container {
  padding: 0;
  margin: 0;
  list-style: none;
  background:#B1B1B1;
  height:600px;
  display: -webkit-box;
  display: -moz-box;
  display: -ms-flexbox;
  display: -webkit-flex;
  display: flex;
  flex-wrap: wrap; /*nowrap | wrap | wrap-reverse;*/
  -webkit-flex-wrap: wrap; /* Safari 6.1+ */
  -mz-flex-wrap: wrap; 
  align-content: stretch;
}


  


.flex-item {
  background: tomato;
  padding: 5px;
  width: 200px;
  height: 150px;
  margin: 10px;
  line-height: 150px;
  color: white;
  font-weight: bold;
  font-size: 3em;
  text-align: center;
}

.flex-item:nth-child(1) {
	flex-grow: 1;
	-webkit-flex-grow: 1;
}

.flex-item:nth-child(2) {
	flex-grow: 1;
	-webkit-flex-grow: 1;
}

.flex-item:nth-child(3) {
	flex-grow: 1;
	-webkit-flex-grow: 1;
}

.flex-item:nth-child(4) {
	flex-grow: 1;
	-webkit-flex-grow: 1;
}

.flex-item:nth-child(5) {
	flex-grow: 1;
	-webkit-flex-grow: 1;
}

.flex-item:nth-child(6) {
	flex-grow: 1;
	-webkit-flex-grow: 1;
	
}