JSFiddle - React, Tailwind, and code Playground
HTML
<div style="--a: #ffc300"></div>
CSS
div {
width: 300px;
height: 300px;
margin: 100px;
background: hsl(var(--a));
--b: hsl(from var(--a) h s calc(l + 20));
border: 20px solid var(--b);
}