JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div id="title"></div>
    <div id="wPlaceHolder"></div>
    <div style="clear:both"></div>
    <div id="bPlaceHolder"></div>
    <div id="content"></div>
</div>

CSS

#container { width:500px; }
#title, #content { background:#333; }
#wPlaceHolder {
    background:#fff;
    height: 40px;
    border: 1px #fff solid;
    -moz-border-radius-bottomleft:10px;
    width: 380px;
    float:left;
    position:absolute;
    left:110px;
}
#bPlaceHolder {
    height:10px;
    background:#333;
    width:400px;
}
#title {
    width: 100px;
    height: 30px;
    -moz-border-radius-topleft: 10px;
    -moz-border-radius-topright: 10px;
    border:1px #333 solid;
    float:left;
}
#content {
    -moz-border-radius-bottomleft: 10px;
    -moz-border-radius-bottomright: 10px;
    -moz-border-radius-topright: 10px;    
    height:100px;
}