JSFiddle - React, Tailwind, and code Playground

HTML

<body id="drop">
    <div class="site-wrapper">
        <div class="site-wrapper-inner">
            <div class="cover-container">
                <div class="inner cover text-center">
                    <h1 class="cover-heading" id="promo-text">Drop file somewhere here.</h1>

                    <p id="progress" hidden="hidden">
                        <progress id="uploadprogress" min="0" max="100" value="0">0</progress>
                    </p>
                </div>
            </div>
        </div>
    </div>
</body>

CSS

a,
a:focus,
a:hover {
    color: #fff;
}


html,
body {
    height: 100%;
    background-color: #333;
}
body {
    color: #fff;
    text-align: center;
    text-shadow: 0 1px 3px rgba(0,0,0,.5);
}

/* Extra markup and styles for table-esque vertical and horizontal centering */
.site-wrapper {
    display: table;
    width: 100%;
    height: 100%; /* For at least Firefox */
    min-height: 100%;
    -webkit-box-shadow: inset 0 0 100px rgba(0,0,0,.5);
    box-shadow: inset 0 0 100px rgba(0,0,0,.5);
}
.site-wrapper-inner {
    display: table-cell;
    vertical-align: top;
}
.cover-container {
    margin-right: auto;
    margin-left: auto;
}

/* Padding for spacing */
.inner {
    padding: 30px;
}


#drop-overlay {
    position: absolute;
    top: 0;
    width:100px;
    height:100px;
    background:url('/img/drop.png') center center no-repeat;
    background-color: rgba(129, 126, 126, .9);
}


/*
 * Header
 */
.masthead-brand {
    margin-top: 10px;
    margin-bottom: 10px;
}

.masthead-nav > li {
    display: inline-block;
}
.masthead-nav > li + li {
    margin-left: 20px;
}
.masthead-nav > li > a {
    padding-right: 0;
    padding-left: 0;
    font-size: 16px;
    font-weight: bold;
    color: #fff; /* IE8 proofing */
    color: rgba(255,255,255,.75);
    border-bottom: 2px solid transparent;
}
.masthead-nav > li > a:hover,
.masthead-nav > li > a:focus {
    background-color: transparent;
    border-bottom-color: #a9a9a9;
    border-bottom-color: rgba(255,255,255,.25);
}
.masthead-nav > .active > a,
.masthead-nav > .active > a:hover,
.masthead-nav > .active > a:focus {
    color: #fff;
    border-bottom-color: #fff;
}

@media (min-width: 768px) {
    .masthead-brand {
        float: left;
    }
    .masthead-nav {
        float: right;
    }
}

.cover {
    padding: 0 20px;
}
.cover .btn-lg {
    padding: 10px 20px;
    font-weight: bold;
}


.mastfoot {
    color: #999; /* IE8 proofing */
    color: rgba(255,255,255,.5);
}

@media (min-width: 768px) {
   ...

JavaScript

var drop = document.getElementById('drop'),
    text = document.getElementById('promo-text');
var textChanged = false;

drop.ondragenter = function () {
        console.log('dragged!');
        if (!textChanged) {
        	text.innerHTML = 'Drop it here!';
            textChanged = true;
        }
        return false;
    };