ribbon.html

<style>
.ribbon {
    overflow: hidden;
    white-space: nowrap;
    position: absolute;
    right: 0;
    top: 0;
    width: 100px;
    height: 100px;
}

.ribbon span {
    position: absolute;
    right: -24px;
    top: 9px;
    background-color: #900;
    border: 1px solid #faa;
    color: #fff;
    display: block;
    font: bold 81.25% 'Helvetica Neue', Helvetica, Arial, sans-serif;
    margin: 1px 0;
    padding: 5px 30px;
    text-align: center;
    text-decoration: none;
    text-shadow: 0 0 5px #444;
    transform: rotate(45deg);
    -webkit-transform: rotate(45deg);
    -moz-transform: rotate(45deg);
    -ms-transform: rotate(45deg);
    -o-transform: rotate(45deg);
    -webkit-box-shadow: 0 0 10px #888;
    -moz-box-shadow: 0 0 10px #888;
}
</style>

<div class="ribbon">
  <a href="#">Fork me on GitHub</a>
</div>