JSFiddle - React, Tailwind, and code Playground

HTML

<div id="triangle"></div>

CSS

body {
  min-height: 2000px;
}
#triangle {
    position: absolute;
    top: 0px;
    right: 0px;
    border-top: 100vw solid #ff0000; /* The height of the triangle */
    border-left: 30vw solid transparent; /* The width of the triangle */
}