JSFiddle - React, Tailwind, and code Playground

HTML

<div class="gradient-demo"></div>

CSS

.gradient-demo {
    background-color: #eee;
    height: 180px;
    width: 320px;    
}
.gradient-demo::before {
    background: #ffffff;
    background: -moz-linear-gradient(left, #ffffff 0%, #999999 100%);
    background: -webkit-gradient(linear, left top, right top, color-stop(0%, #ffffff), color-stop(100%, #999999));
    background: -webkit-linear-gradient(left, #ffffff 0%, #999999 100%);
    background: -o-linear-gradient(left, #ffffff 0%, #999999 100%);
    background: -ms-linear-gradient(left, #ffffff 0%, #999999 100%);
    background: linear-gradient(to right, #ffffff 0%, #999999 100%);
    filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#ffffff', endColorstr='#999999', GradientType=1);
    content: "";
    display: block;
    height: 100%;
    width: 3px;
}