JSFiddle - React, Tailwind, and code Playground

HTML

<div class="content">
    Some Content
</div>
<div id="toptriangle"></div>

CSS

body {
    color: white;
    background-color: #666666;
}

.content {
    text-align: center;
}

#toptriangle {
    position: relative;
    width: 0px;
    height: 0px;
    top: 100px;
    left: -10px;
    border-right: 500px solid white;
    border-top: 300px solid transparent;
    border-left: 500px solid white;
    border-bottom: 400px solid white;
}