JSFiddle - React, Tailwind, and code Playground

HTML

<div class="caixa"></div>

CSS

.caixa{
    width:100px;
    height:100px;
    border-top: 14px solid red;
    position: relative;
}

.caixa::after {
    content: "";
    position: absolute;
    bottom: 0; top: 0px; left: 0; right: 0;
    border-right: 14px solid blue;
}