CSS Underglow Effect

HTML

<header>
    <h1>CSS Underglow Effect</h1>
</header>
<span id="shadow">&nbsp;</span>

CSS

body {
    background: #eee;
    margin: 0px;
    font-family: sans-serif;
}

header {
 
    border-bottom: solid 1px #e9e9e9;
    padding: 10px;
    padding-left: 40px;
    margin-bottom: 80px;
}

#shadow {
    background-image: -webkit-radial-gradient(50% 0%, ellipse farthest-side, rgba(0, 180, 255, 0.25) 0%, rgba(0, 180, 255, 0) 100%);
    background-image: -moz-radial-gradient(50% 0%, ellipse farthest-side, rgba(0, 180, 255, 0.25) 0%, rgba(0, 180, 255, 0) 100%);
    background-image: -ms-radial-gradient(50% 0%, ellipse farthest-side, rgba(0, 180, 255, 0.25) 0%, rgba(0, 180, 255, 0) 100%);
    background-image: -o-radial-gradient(50% 0%, ellipse farthest-side, rgba(0, 180, 255, 0.25) 0%, rgba(0, 180, 255, 0) 100%);
    background-image: radial-gradient(50% 0%, ellipse farthest-side, rgba(0, 180, 255, 0.25) 0%, rgba(0, 180, 255, 0) 100%);
    width: 100%;
    height: 12px;
    display: block;
    float: center;
    position: relative;
    top: -80px;
    z-index: -99;
}