One-line: a single on/off button — use for formatting-style controls (bold, mute, pin), not for settings (that is Switch).

```jsx
<Toggle aria-label="Bold" defaultPressed><BoldIcon /></Toggle>
<Toggle variant="outline" size="sm">Weekly</Toggle>
```

Two variants: \`default\` (transparent until hovered) and \`outline\` (bordered, matches Button outline). Pressed = \`--input\` at 64%.
