Edit in JSFiddle

<div class="flex-container">
<div class="flex-item1">flex item 1</div>
<div class="flex-item2">flex item 2</div>
<div class="flex-item3">flex item 3</div>
</div>
<button id="flex-start" class="btn btn-default">flex-start</button>
<button id="flex-end" class="btn btn-default">flex-end</button>
<button id="center" class="btn btn-default">center</button>
<button id="baseline" class="btn btn-default">baseline</button>
<button id="stretch" class="btn btn-default">stretch</button>

.flex-container {
    display: -webkit-flex;
    display: flex;
    justify-content: center;
    width:100%;
    height: 250px;
    background-color: white;
    border: 1px solid #ddd;
    margin-bottom:20px;

}

.flex-item1 {
    background-color: DeepSkyBlue;
    width: 100px;
    margin: 5px;
    font-size:2em;
}
.flex-item2 {
    background-color: pink;
    width: 150px;

    margin: 5px;
}
.flex-item3 {
    background-color: green;
    width: 250px;
    margin: 5px;
    line-height:5em;
}

var container = $(".flex-container");
$(document).on('click','button',function(){
    var id = $(this).attr('id');
    container.css('align-items',id);
});