---
category: Foundations
---

A 1px `--border` — the measured seam, and the reference's most-used border by a
factor of two. `strong` is `--border-strong` and belongs where a divider has to
be *seen*: between two groups of rows, not between two rows.

Unlike the hairline packs, a rule here is not the elevation model. This pack has
three named shadows doing three different jobs, and a rule is for structure
inside a surface that is already separated.

```tsx
<Rule />
<Rule tone="strong" />
```