JSFiddle - React, Tailwind, and code Playground

HTML

<div class="header-wrapper">
    <div class="part1"></div>
</div>

CSS

.header-wrapper .part1::after {
    content:'';
    width: 0;
    height: 0;
    border-left: solid 48.35px #f21e1e;
    border-bottom: solid 48.35px transparent;
    border-top: solid 48.35px transparent;
}