JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap.min.css">
<div class="col-xs-12 widget-header-div">

    <div class="col-xs-12 col-sm-6 col-lg-3 widget-header-item">
        <div class="panel panel-primary pmd-z-depth">
            <div class="panel-heading">Box 1</div>

            <div class="panel-body">
                <table class="col-md-12 text-left">
                    <tr>
                        <td>Key</td>
                        <td>Value</td>
                    </tr>
                    <tr>
                        <td>Key</td>
                        <td>Value</td>
                            <td>Value</td>
                    </tr>
                    <tr>
                        <td>Key</td>
                        <td>Value</td>
                    </tr>
                </table>
            </div>
        </div>
    </div>

    <div class="col-xs-12 col-sm-6 col-lg-3 widget-header-item">
        <div class="panel panel-primary pmd-z-depth">
            <div class="panel-heading">Box 2</div>
            <div class="panel-body">
               <table class="col-md-12 text-left">
                    <tr>
                        <td>Key</td>
                        <td>Value</td>
                    </tr>
                </table>
            </div>
        </div>
    </div>

    <div class="col-xs-12 col-lg-6 widget-header-item">
        <div class="panel panel-primary pmd-z-depth">
            <div class="panel-heading">Box 3</div>
            <div class="panel-body">
            <p>Larger body of text here</p>
            <p>Larger body of text here</p>
            <p>Larger body of text here</p>
            <p>Larger body of text here</p>
            <p>Larger body of text here</p>
            <p>Larger body of text here</p>
            </div>
        </div>
    </div>

</div>

CSS

.widget-header-div, .widget-header-div > div[class*='col-'] {  
    display: -webkit-box;
    display: -moz-box;
    display: -ms-flexbox;
    display: -webkit-flex;
    display: flex;
    flex:1 1 auto;
}