Edit in JSFiddle

<div class="flex-container row align-content-start bg">
	  <div class="flex-item big">1</div>
	  <div class="flex-item">2</div>
	  <div class="flex-item">3</div>
	  <div class="flex-item">4</div>
	  <div class="flex-item">5</div>
	  <div class="flex-item">6</div>
	  <div class="flex-item">7</div>
	  <div class="flex-item">8</div>
	  <div class="flex-item">9</div>
	  <div class="flex-item">10</div>
	  <div class="flex-item">11</div>
	  <div class="flex-item small-text">start</div>
</div>
<br>
<div class="flex-container row align-content-end bg">
	  <div class="flex-item big">1</div>
	  <div class="flex-item">2</div>
	  <div class="flex-item">3</div>
	  <div class="flex-item">4</div>
	  <div class="flex-item">5</div>
	  <div class="flex-item">6</div>
	  <div class="flex-item">7</div>
	  <div class="flex-item">8</div>
	  <div class="flex-item">9</div>
	  <div class="flex-item">10</div>
	  <div class="flex-item">11</div>
	  <div class="flex-item small-text">end</div>
</div>
<br>
<div class="flex-container row align-content-center bg">
	  <div class="flex-item big">1</div>
	  <div class="flex-item">2</div>
	  <div class="flex-item">3</div>
	  <div class="flex-item">4</div>
	  <div class="flex-item">5</div>
	  <div class="flex-item">6</div>
	  <div class="flex-item">7</div>
	  <div class="flex-item">8</div>
	  <div class="flex-item">9</div>
	  <div class="flex-item">10</div>
	  <div class="flex-item">11</div>
	  <div class="flex-item small-text">center</div>
</div>
<br>
<div class="flex-container row align-content-stretch bg">
	  <div class="flex-item big">1</div>
	  <div class="flex-item">2</div>
	  <div class="flex-item">3</div>
	  <div class="flex-item">4</div>
	  <div class="flex-item">5</div>
	  <div class="flex-item">6</div>
	  <div class="flex-item">7</div>
	  <div class="flex-item">8</div>
	  <div class="flex-item">9</div>
	  <div class="flex-item">10</div>
	  <div class="flex-item">11</div>
	  <div class="flex-item small-text">stretch</div>
</div>
<br>
<div class="flex-container row align-content-space-between bg">
	  <div class="flex-item big">1</div>
	  <div class="flex-item">2</div>
	  <div class="flex-item">3</div>
	  <div class="flex-item">4</div>
	  <div class="flex-item">5</div>
	  <div class="flex-item">6</div>
	  <div class="flex-item">7</div>
	  <div class="flex-item">8</div>
	  <div class="flex-item">9</div>
	  <div class="flex-item">10</div>
	  <div class="flex-item">11</div>
	  <div class="flex-item small-text">sp-bet</div>
</div>
<br>
<div class="flex-container row align-content-space-around bg">
	  <div class="flex-item big">1</div>
	  <div class="flex-item">2</div>
	  <div class="flex-item">3</div>
	  <div class="flex-item">4</div>
	  <div class="flex-item">5</div>
	  <div class="flex-item">6</div>
	  <div class="flex-item">7</div>
	  <div class="flex-item">8</div>
	  <div class="flex-item">9</div>
	  <div class="flex-item">10</div>
	  <div class="flex-item">11</div>
	  <div class="flex-item small-text">sp-ar</div>
</div>

.flex-container {
  padding: 0;
  margin: 0;
  -ms-box-orient: horizontal;
  display: -webkit-box;
  display: -moz-box;
  display: -ms-flexbox;
  display: -moz-flex;
  display: -webkit-flex;
}
.align-content-start {
	align-content: flex-start; 
}

.align-content-end {
	align-content: flex-end; 
}

.align-content-center {
	align-content: center; 
}

.align-content-stretch {
	align-content: stretch; 
}

.align-content-space-between {
	align-content: space-between; 
}

.align-content-space-around {
	align-content: space-around; 
}


.row           { 
  -webkit-flex-direction: row; 
  flex-direction: row;
  flex-wrap: wrap;
}

.flex-item {
  background: deepskyblue;
  padding: 5px;
  width: 55px;
  margin: 5px;
  line-height: 50px;
  color: white;
  font-weight: bold;
  font-size: 2em;
  text-align: center;
}
.bg {
	background: #9E9E9E;
	height: 200px;
}
.small-text{
	font-size: 1em;
}