JSFiddle - React, Tailwind, and code Playground

HTML

<div class="box">
    <div class="corner">
        <span href="#">Best Ribbon around</span>
    </div>
    <img src="http://lorempixel.com/250/300/sports/1/">
</div>

CSS

body {background:yellow;padding:50px}

.box { position:relative;overflow:hidden;}
.box img {
    border:2px solid green;
    padding: 3%;
    background: #ccc;
}

.corner {
    background-color: #a00;
    overflow: hidden;
    position: absolute;
    left: -4em;
    top: 2.5em;
    -moz-transform: rotate(-45deg);
    -webkit-transform: rotate(-45deg);
    transform: rotate(-45deg);
    z-index: 100;

}
.corner span {
    border: 1px solid #faa;
    color: #fff;
    display: block;
    font-size:.8em;
    font-weight:bold;
    padding: 0.5em 4em;
    text-align: center;
    text-decoration: none;
    text-shadow: 1px 1px 1px #000;
    z-index: 100;
}