<div class="swatch primary"></div>
<div class="swatch"></div>
<div class="swatch"></div>
@layer demo {
  :root {
    --base-color: yellow; /* change me */
  }
  
  .swatch.primary {
    background: var(--base-color);
  }
  
  .swatch:nth-child(2) {
    background: oklch(from var(--base-color) l c calc(h - 120));
  }
  
  .swatch:nth-child(3) {
    background: oklch(from var(--base-color) l c calc(h + 120));
  }
}

@layer demo.support {
  * {
    box-sizing: border-box;
    margin: 0;
  }

  html {
    block-size: 100%;
    color-scheme: dark light;
  }

  body {
    min-block-size: 100%;
    font-family: system-ui, sans-serif;

    display: grid;
    grid-template-rows: repeat(3, 1fr);
  }
}

External CSS

  1. https://codepen.io/argyleink/pen/jOXdPjO.css

External JavaScript

This Pen doesn't use any external JavaScript resources.