JSFiddle - React, Tailwind, and code Playground

HTML

<div class="test">
</div>

CSS

.test {
    position: absolute;
    left: 20px;
    top: 20px;
    width: 200px;
    height: 200px;
    border-style: solid;
    border-width: 20px 0px;
    border-image-source: linear-gradient(90deg, rgba(255,255,255,0), rgba(255,255,255,1), rgba(255,255,255,0));
    border-image-slice: 10;
    border-image-repeat: stretch;
    box-shadow: 0px 0px 10px black;
}

body {
    background-color: lightblue;
}