smooth-shadows

Smooth Shadows

Generate production-quality layered smooth box-shadows that look like the beloved (now offline) shadows.brumm.af tool and the current smoothshadows.com successor.

This skill implements the technique from Tobias Ahlin's canonical article and gives agents the same parameters the original UI exposed (Style, Opacity, Blur, Layered shadows count, Vertical/Horizontal distance, Colors).

Quick Start

/smooth-shadows soft lift on a dashboard card, vertical 32px, 5 layers, blur around 24

/smooth-shadows --style sharp --layers 4 --vertical 16 --output css

Natural language or explicit flags both work.

The skill will return the full box-shadow value (and usually a Tailwind version too).

Parameters (match the original UI)

Control	Flag / Param	Default	Notes
Style	--style	soft	soft (gentle, larger blur), sharp (crisper, stronger inner layers), linear (even steps)
Layered shadows	--layers, -l	5	3–6 is the sweet spot for most UIs. More = softer spread but can get muddy.
Vertical distance	--vertical, -v	32	The "lift" / main y offset of the largest layer (px).
Horizontal	--horizontal, --h-dist	0	Side offset (rarely needed, but supported).
Blur	--blur	24	Base/max blur radius. The generator scales it across layers.
Opacity	--opacity	0.08	Base alpha for the shadow color (very low = modern & subtle).
Color	--color	#030712	Any hex. The same color is used for every layer with varying alpha.
Output	--output	raw	raw (just the value), css (full box-shadow: ...;), tailwind (arbitrary shadow-[...]).
Dark mode	--dark	false	Boosts opacity for dark surfaces (or use a lighter color).

Workflow

1. Understand the request
   Extract (or ask for) the visual intent: how "lifted" does it feel? Soft & dreamy, crisp & defined, or even linear? Any dark mode context?

2. Choose good defaults or map the request

   • Soft card / modal lift → style=soft, 4–6 layers, vertical 24–40, low opacity (0.06–0.10)
   • Crisp button or pressed state → style=sharp, 3–4 layers, smaller vertical
   • Subtle background separation → style=linear or soft, 3 layers, very low opacity

3. Generate (preferred: use the deterministic script)
   Call the bundled script for pixel-perfect, repeatable output instead of the model inventing numbers.

4. Present & refine
   Return:

   • The raw box-shadow value
   • A ready <div style="box-shadow: ..."> or CSS rule snippet
   • Tailwind arbitrary value version
   • One-sentence note on why these numbers (e.g. "5 layers with geometric progression gives the classic soft falloff")

5. Offer variations
   "Want a slightly more dramatic version? I can give you vertical 48 / 6 layers."
   "Dark surface? I can regenerate with --dark."

Scripts

scripts/generate-smooth-shadow.js

The single source of truth for the layer math. Run it directly for perfect reproducibility.

From inside the installed skill (recommended form):

node <this-skill-dir>/scripts/generate-smooth-shadow.js --vertical 32 --layers 5 --style soft --opacity 0.08 --blur 24 --color '#030712'
node <this-skill-dir>/scripts/generate-smooth-shadow.js -v 16 -l 3 --style sharp --output css
node <this-skill-dir>/scripts/generate-smooth-shadow.js --vertical 40 --layers 6 --style linear --dark --output tailwind

Full help:

node <this-skill-dir>/scripts/generate-smooth-shadow.js --help

The script also exports generateSmoothShadow(params) so an agent that has located the skill directory can require() it programmatically if desired.

Resolve script paths relative to this skill directory when installed.

References

• references/algorithm.md — The Tobias Ahlin technique, how the three styles map to alpha & blur curves, and the concrete examples the generator is based on.
• references/examples.md — Ready-to-copy box-shadow declarations for common UI patterns (with the exact params that produced them).

Integration with Other Skills

• Pairs extremely well with make-interfaces-feel-better (which explicitly recommends "Use layered box-shadow with transparency" to avoid hard borders).
• Use the output with any frontend-design / impeccable flow when building cards, modals, navigation, etc.
• For Figma: the values translate directly to multiple DROP_SHADOW effects on a node (see figma-use effect-style patterns for the API shape). The skill can also just emit the numbers for you to apply manually.

Troubleshooting

"The shadow feels too heavy / has hard edges"

Reduce --layers to 3–4 or lower --opacity. The classic look uses surprisingly low opacity spread across several layers.

"I need it for a dark surface"

Add --dark (the script increases opacity). You can also pass a lighter color (e.g. a soft warm gray) for a different aesthetic.

"The numbers don't match smoothshadows.com exactly"

The generator targets the visual character of the original tool using the public algorithm. Small differences in the exact easing curve are normal; the result will still look smooth and professional. Tweak vertical/blur/layers by hand if you need pixel-perfect parity with a specific screenshot.

"I want a full elevation scale (xs → 2xl)"

Run the generator several times with increasing --vertical values (e.g. 4, 8, 16, 32, 48) and the same style. Or ask the skill: "give me a 6-step smooth shadow elevation scale".

"Tailwind output looks ugly"

The arbitrary value is intentionally ugly in source but produces the correct runtime shadow. Extract it to a component or @layer utilities if you will reuse it often.

Why This Exists

Single box-shadow values almost always look cheap or "computer-y". Layering several shadows with carefully increasing offset + blur (and controlled alpha) is one of the highest-leverage micro-details in UI craft. This skill makes that technique trivial and repeatable for agents.

Credit: technique by Tobias Ahlin, original generator by Philipp Brumm, current web UI at smoothshadows.com.