Edit in JSFiddle

<p class="bg-title">
flex-wrap: normal
</p>
<ul class="flex-container row">
  <li class="flex-item">1</li>
  <li class="flex-item">2</li>
  <li class="flex-item">3</li>
  <li class="flex-item">4</li>
  <li class="flex-item">5</li>
  <li class="flex-item">6</li>
  <li class="flex-item">7</li>
  <li class="flex-item">8</li>
  <li class="flex-item">9</li>
  <li class="flex-item">10</li>
  <li class="flex-item">11</li>
  <li class="flex-item">12</li>
  <li class="flex-item">13</li>
</ul>
<p class="bg-title">
flex-wrap: wrap
</p>
<ul class="flex-container row-wrap">
  <li class="flex-item">1</li>
  <li class="flex-item">2</li>
  <li class="flex-item">3</li>
  <li class="flex-item">4</li>
  <li class="flex-item">5</li>
  <li class="flex-item">6</li>
  <li class="flex-item">7</li>
  <li class="flex-item">8</li>
  <li class="flex-item">9</li>
  <li class="flex-item">10</li>
  <li class="flex-item">11</li>
  <li class="flex-item">12</li>
  <li class="flex-item">13</li>
</ul>
<p class="bg-title">
flex-wrap: wrap-reverse
</p>
<ul class="flex-container row-wrap-reverse">
  <li class="flex-item">1</li>
  <li class="flex-item">2</li>
  <li class="flex-item">3</li>
  <li class="flex-item">4</li>
  <li class="flex-item">5</li>
  <li class="flex-item">6</li>
  <li class="flex-item">7</li>
  <li class="flex-item">8</li>
  <li class="flex-item">9</li>
  <li class="flex-item">10</li>
  <li class="flex-item">11</li>
  <li class="flex-item">12</li>
  <li class="flex-item">13</li>
</ul>
.flex-container {
  padding: 0;
  margin: 0;
  list-style: none;
  
  -ms-box-orient: horizontal;
  display: -webkit-box;
  display: -moz-box;
  display: -ms-flexbox;
  display: -moz-flex;
  display: -webkit-flex;
  display: flex;
}

.row-wrap           { 
  -webkit-flex-direction: row; 
  flex-direction: row;
  flex-wrap: normal;
}
.row-wrap li           { 
  background: deepskyblue;
}

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

.row-wrap-reverse           { 
  -webkit-flex-direction: row; 
  flex-direction: row;
  flex-wrap: wrap-reverse;
}
.row-wrap-reverse li           { 
  background: lightgreen;
}
.flex-item {
  background: tomato;
  padding: 5px;
  width: 50px;
  height: 50px;
  margin: 5px;
  
  line-height: 50px;
  color: white;
  font-weight: bold;
  font-size: 2em;
  text-align: center;
}
.bg-title{
	background: black;
	color: white;
	display:inline;
}