feat(breakpoints): document preset viewport helpers, low-level container helpers, and exported types for breakpoints

readme.md

@@ -110,7 +110,7 @@ const myStyles = litCss`
 `;
 ```
 
-**Available breakpoint helpers:**
+**Preset viewport helpers** (emit both `@media` and `@container wccToolsViewport`):
 
 - `cssForDesktop(css)` - Styles for 1600px and above
 - `cssForNotebook(css)` - Styles for 1240px and below
@@ -118,6 +118,37 @@ const myStyles = litCss`
 - `cssForPhablet(css)` - Styles for 600px and below
 - `cssForPhone(css)` - Styles for 400px and below
 
+**Low-level helpers** for custom constraints and component-scoped containers:
+
+```typescript
+import { breakpoints } from '@design.estate/dees-domtools';
+import { css as litCss } from 'lit';
+
+// Viewport-level with custom constraints (emits @media + @container wccToolsViewport)
+breakpoints.cssForCustom({ maxWidth: 800 })(litCss`.box { padding: 8px; }`)
+
+// Component-level — targets a named container (no @media fallback)
+breakpoints.cssForContainer(
+  litCss`.grid { columns: 1; }`,
+  '(max-width: 600px)',
+  'my-component'  // CSS container-name
+)
+
+// Component-level with custom constraints (curried)
+breakpoints.cssForCustomContainer({ maxWidth: 500 }, 'my-component')(litCss`
+  .grid { gap: 8px; }
+`)
+
+// Generate containment styles for :host (used by @containerResponsive decorator)
+breakpoints.containerContextStyles('my-component')
+// → :host { container-type: inline-size; container-name: my-component; }
+```
+
+**Exported types:**
+
+- `ICssForConstraints` — `{ maxWidth?: number; minWidth?: number }`
+- `TViewport` — `'native' | 'desktop' | 'tablet' | 'phablet' | 'phone'`
+
 ### Theme Management
 
 Automatic theme detection with system preference support: