Font Awesome 3.0.2 Fiddle

HTML

<link rel="stylesheet" href="http://cdnjs.cloudflare.com/ajax/libs/font-awesome/3.0.2/css/font-awesome.css">
<span><i class="icon-check icon-3x"></i></span>

<span>
<i>d</i>
</span>

CSS

html, body, div, canvas {
    margin: 0;
    padding: 0;
}
span {

    line-height: 40%;
}
i {
    border: 1px solid red;
    border: 1px solid green;
    padding: 0px;
    margin: 0px;
    display: inline-block;
    width: auto;
    height: auto;
    line-height: inherit;
    vertical-align: baseline;
    background-color: red;
}