Edit in JSFiddle

#container {
   display:flex;
   flex-direction:row;
   justify-content:center;
   align-items:center;
   height:150px;
   width:350px;
   border:1px solid #cccccc;   
}
.item1 {
   height:100px;
   width:150px;   
   border:1px solid #cccccc;    
}
.item2 {
   height:50px;
   width:150px;   
   /* 覆寫了父元素的 align-items */
   align-self:flex-end; 
   border:1px solid #cccccc;     
}
div {
   margin:5px;
}

<div id="container">
     <div class="item1">
        hello!     
     </div>
     <div class="item2">
        test     
     </div>
</div>