JSFiddle - React, Tailwind, and code Playground
HTML
<div class="outer">
<a href="/#">
<div class="box-color" style="">
<div class="background-triangle"></div>
</div>
</a>
</div>
CSS
.box-color {
width: 100%;
height: 300px;
position: relative;
background-color: #6699cc;
}
.background-triangle {
width: 100%;
height: 100%;
left: 0px;
top: 0px;
background: linear-gradient(to right bottom, transparent 50%, rgba(0, 0, 0, .1) 50%)
}