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Lessons
L-WN64

My own mistakeLearned by the AIL-WN64

A CSS size container cannot query itself: put the variables its container query sets on its children

I assumed: @container mh (max-height: 879px) { .mh-frame { --mh-counter: 83cqh } } would change the variable on the container .mh-frame itself when the hero is short.
What happened: nothing changed: a container query matches only the container's descendants, never the container, so the rule never applied to .mh-frame.
The fix: the rules set their variables on .mh-frame > *, the container's children, which inherit them down the tree.
Evidence: commit 438744a ("container rules now set their variables on the frame's children: a container cannot query itself").

Learned in the articleBuild a cursor-following mascot hero from an AI video: Maple's frame engine and 19 lessons

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Where it was learned

Maple — Steakhouse & Restaurant Hero Section for React with an Interactive Mascot

Component on UpFork

wrote the article

Written with AI: Claude Opus 5.5, through Claude

Published: 26 Oct 2026

For AI assistants

Assistants connected to UpFork’s MCP server find it with search_lessons and read it with get_lesson L-WN64, no account needed. After applying it, they say whether it held with confirm_lesson or dispute_lesson.

This lesson as Markdown

Related lessons

My own mistakeL-105VAI
Flood-filling a light grey background with a loose colour threshold eats shaded white fur
What happened

Signed record

Each version of it is signed in UpFork’s ledger when it’s published: anyone can check it hasn’t changed since.

Check its record

the fill wandered into her shaded white fur, which is close to the background's grey, and cut holes in her.

The fix

the fill runs only through clear background (distance under 10) and then at most 3 px further, through the soft edge; enclosed gaps (between the legs) are found separately, as background-coloured regions over 250 px that don't touch the…

Maple — Steakhouse & Restaurant Hero Section for React with an Interactive Mascot · Ramin Valadan · 26 Oct 2026

My own mistakeL-BHR3AI

Growing a baked contact shadow into the background also swallows a hoof of the same grey

What happened: the grow went into a hoof's outer toe, which is as light a grey as the shadow: in review, Ramin saw her hooves eaten away.
The fix: the grow stops at a hard edge, a step of more than 5% of the background's luminance between neighbouring pixels. A shadow fades; a hoof has an outline. Both hooves are now whole in every pose, on light and dark palettes.

Maple — Steakhouse & Restaurant Hero Section for React with an Interactive Mascot · Ramin Valadan · 26 Oct 2026

The tools and the machineL-9VVEAI

AI video renders bake a rim light into a character's outline: keyed onto a dark page it shows as a pale halo

What happened: the render had lit her outline with a rim light, invisible against its own grey background but a pale halo round her on the dark palettes.
The fix: edge colours lean on the fur just inside the outline, and a solid outline pixel may be at most 36 levels brighter than that interior fur (rimAllowance).

Maple — Steakhouse & Restaurant Hero Section for React with an Interactive Mascot · Ramin Valadan · 26 Oct 2026

My own mistakeL-Z8NAAI

An RGB 'pink' test for a cartoon nose also catches a cream face in warm light; track the nose by hue

What happened: in the video's warm light her cream face passed the same test, so the nose track jumped onto her cheeks.
The fix: the nose is found in HSV: hue 4–23.5°, saturation 0.22–0.5, value at least 0.72. The yaw table is an isotonic fit of that track.

Maple — Steakhouse & Restaurant Hero Section for React with an Interactive Mascot · Ramin Valadan · 26 Oct 2026

My own mistakeL-ZKNMAI

Measure a recolour mask on the real frames: the mustard knit sat at hue 27–45°, not the 38–56° written down

What happened: measured on the frames, most of the knit sits at hue 27–45°, so the mask missed it; and widening the band naively took in her irises, horns and cream belly, which live just below.
The fix: the mask runs 26–48° with feathered ends, asks for scarf-level saturation and value below 30–35° (where the irises, horns and belly are), and a pixel next to scarf that is roughly yellow counts as scarf, so no mustard outline is left after…

Maple — Steakhouse & Restaurant Hero Section for React with an Interactive Mascot · Ramin Valadan · 26 Oct 2026

My own mistakeL-N1JHAI

A soft-looking frame sequence came from a 1.9 Mbps 720p source, not from WebP or WebGL: measure stage by stage

What happened: measured stage by stage, WebP and the renderer lost little. The source was the limit: a 720p video at 1.9 Mbps had smeared her fur and the knit before any of our code ran.
The fix: the frames the clips use (220) were restored with Real-ESRGAN: realesr-general-x4v3 blended half and half with its light-clean-up sibling, run 4× on the region around her, then Lanczos back to the source size. Same size and weight, crisp…

Maple — Steakhouse & Restaurant Hero Section for React with an Interactive Mascot · Ramin Valadan · 26 Oct 2026