JSFiddle - React, Tailwind, and code Playground

HTML

<div class="root">
    
    <div class="slash">
    </div>
</div>

CSS

.root {
    border: 1px solid gray;
    background-color: yellow;
    width: 100%;
    height: 200px;
    position: relative;
    overflow: hidden;
}

.slash {
    width: 200%;
    height: 200%;
    background-color: white;
    border: 5px solid gray;
    transform: rotate(45deg) translateY(100%);
}