Try it Live

​x
 
<!DOCTYPE html>
<html>
 <head>
  <style>
  .flexbox-container {
    margin:10px;    
    display: flex;
    flex-wrap: wrap-reverse;
    background-color: yellow;
  }
  
  .child-items {
    padding: 25px 0;
    margin: 5px;
    width:60px;
    height:80px;
    text-align: center;
    border:1px solid olive;
    background-color: tomato;
  }
  </style>
 </head>
 <body>
  <div class="flexbox-container">
    <div class="child-items">Item 1</div>
    <div class="child-items">Item 2</div>
    <div class="child-items">Item 3</div>
    <div class="child-items">Item 4</div>
    <div class="child-items">Item 5</div>
    <div class="child-items">Item 6</div>
    <div class="child-items">Item 7</div>
    <div class="child-items">Item 8</div>
    <div class="child-items">Item 9</div>
    <div class="child-items">Item 10</div>
    <div class="child-items">Item 11</div>  
  </div>
 </body>
</html>
​