A box with a thick colored line on its left is the most common look on AI-made sites. Seen once, every site looks like the same AI site, which is exactly the impression these sites avoid. After the site owner judged it unfitting on KRDS (“colored bands inside boxes look wrong”), it was removed from all four packs.
A machine check blocks it. check-stripes, part of design:audit (= check-stripes + check-ai-tells), resolves the built styles with each pack’s color values and counts two things in both light and dark modes: side stripes (left or top border painted in an accent color) and colored heading bars (a heading element with an accent background). A border that goes around all four sides is not a stripe and is not counted. Anything above zero also stops a deploy.
Emphasis comes from weight, size, spacing and steps of grey instead. For example, the KRDS summary box is a grey fill with no border, and the urgent care card is a 2px dark border with a large title.
When to use
Think of it when you want a notice to stand out and reach for a color on one side of the box, or when drawing notice boxes for a new pack.