device-cmyk is a browser polyfill that brings support for CMYK colors into your webpage. It's a simple script tag and your page magically supports color: device-cmyk(1 0 0 0); in your CSS.

<script src="https://unpkg.com/device-cmyk@latest/dist/device-cmyk.polyfill.js"></script>

<style>
    body {
        background-color: device-cmyk(0 1 0 0); /* Magenta */
    }
</style>