Penumbra

Penumbra builds box shadows the way light actually falls: several stacked shadows with increasing blur and decreasing opacity, tinted toward the background color instead of pure black. Pick a light angle, elevation level and background, and it outputs a CSS box-shadow value, a Tailwind theme extension and Figma effect styles.

It's for front-end developers and designers who want cards and dialogs to look lifted rather than smudged. The code is MIT licensed and can be self-hosted or run as an npm command-line tool. The caveat: layered shadows with five or more layers cost slightly more to render, so be careful on long scrolling lists on low-end phones.