Even though the above answer appears to be correct, I wanted to add a (hopefully) more readable example that also stays in 3 columns form at different widths:
.flex-row-container {_x000D_
background: #aaa;_x000D_
display: flex;_x000D_
flex-wrap: wrap;_x000D_
align-items: center;_x000D_
justify-content: center;_x000D_
}_x000D_
.flex-row-container > .flex-row-item {_x000D_
flex: 1 1 30%; /*grow | shrink | basis */_x000D_
height: 100px;_x000D_
}_x000D_
_x000D_
.flex-row-item {_x000D_
background-color: #fff4e6;_x000D_
border: 1px solid #f76707;_x000D_
}
_x000D_
<div class="flex-row-container">_x000D_
<div class="flex-row-item">1</div>_x000D_
<div class="flex-row-item">2</div>_x000D_
<div class="flex-row-item">3</div>_x000D_
<div class="flex-row-item">4</div>_x000D_
<div class="flex-row-item">5</div>_x000D_
<div class="flex-row-item">6</div>_x000D_
</div>
_x000D_
Hope this helps someone else.