JSFiddle - React, Tailwind, and code Playground

HTML

<div class='a'></div>
<div class='b'></div>

CSS

body {
    position: relative;
}
.a {
    position: absolute;
    left: 100px;
    top: 100px;
    width: 100px;
    height: 100px;
    background: #777;
}
.b {
    position: absolute;
    display: none;
    background: red;
}

JavaScript

$(function() {
    $('.a').live('mouseover', function(e) {
        $('.b').offset({'left': $(this).offset().left, 
                        'top': $(this).offset().top})
               .width($(this).outerWidth())
               .height($(this).outerHeight())
               .show();
    });
    $('.b').live('mouseout', function(e) {
        $(this).hide();
    });
});