fix: let the doc bottom navigation wrap on narrow viewports

.lycheeignore

@@ -27,3 +27,6 @@ dist/(.*/)?404((/index)?\.html|/)$
 # Oracle pages return 403 when connected
 ^https://www\.mysql\.com/
 ^https://www\.oracle\.com/
+
+# NVD pages time out when requested from CI runners
+^https://nvd\.nist\.gov/

docs/design-system.md

@@ -91,3 +91,13 @@ Colors are defined using OKLCH color space with `light-dark()` for theme switchi
 | `xs` | < 768px        | `--xs-only`            |
 | `md` | 768px – 1439px | `--md-only`, `--md-up` |
 | `lg` | >= 1440px      | `--lg-up`, `--lg-down` |
+
+## Doc Bottom Navigation
+
+`<DocBottomNav>` closes a doc page with links to the previous and next page in a single
+flex row. The row uses `flex-wrap: wrap-reverse`, so when the two titles cannot sit side
+by side the _Next_ link wraps onto its own line above _Previous_ instead of overflowing
+the page. On wider screens both links stay side by side on one line.
+
+The DOM order stays previous-then-next, so keyboard and screen reader order is unchanged
+when the row wraps.

src/components/patterns/DocBottomNav/DocBottomNav.css

@@ -6,6 +6,16 @@
     margin-top: var(--space-8);
     padding-top: var(--space-6);
     border-top: 1px solid var(--color-border-secondary);
+    flex-wrap: wrap;
+  }
+
+  .doc-nav__link--prev,
+  .doc-nav__link--next {
+    flex-grow: 1;
+
+    svg {
+      flex-shrink: 0;
+    }
   }
 
   .doc-nav__link--next {

tests/e2e/doc-bottom-nav.spec.ts

@@ -0,0 +1,54 @@
+import { test, expect } from '@playwright/test';
+
+// Regression coverage for https://github.com/expressjs/expressjs.com/issues/2486
+const DOC_PATH = '/en/guide/migrating-4/';
+
+test.describe('Doc bottom navigation', () => {
+  test('should not overflow horizontally on a narrow viewport', async ({ page }) => {
+    await page.setViewportSize({ width: 400, height: 900 });
+    await page.goto(DOC_PATH);
+
+    const nav = page.locator('.doc-nav');
+    await expect(nav).toBeVisible();
+
+    const overflow = await nav.evaluate((el) => el.scrollWidth - el.clientWidth);
+    expect(overflow).toBeLessThanOrEqual(1);
+  });
+
+  test('should move the next link above the previous link when they cannot share a line', async ({
+    page,
+  }) => {
+    await page.setViewportSize({ width: 400, height: 900 });
+    await page.goto(DOC_PATH);
+
+    const prev = page.locator('.doc-nav__link--prev');
+    const next = page.locator('.doc-nav__link--next');
+
+    await expect(prev).toBeVisible();
+    await expect(next).toBeVisible();
+
+    const prevBox = await prev.boundingBox();
+    const nextBox = await next.boundingBox();
+
+    if (!prevBox || !nextBox) {
+      throw new Error('expected both doc nav links to be laid out');
+    }
+
+    expect(nextBox.y + nextBox.height).toBeLessThanOrEqual(prevBox.y);
+  });
+
+  test('should keep both links on a single line on a wide viewport', async ({ page }) => {
+    await page.setViewportSize({ width: 1400, height: 900 });
+    await page.goto(DOC_PATH);
+
+    const prevBox = await page.locator('.doc-nav__link--prev').boundingBox();
+    const nextBox = await page.locator('.doc-nav__link--next').boundingBox();
+
+    if (!prevBox || !nextBox) {
+      throw new Error('expected both doc nav links to be laid out');
+    }
+
+    expect(nextBox.y).toBeCloseTo(prevBox.y, 0);
+    expect(nextBox.x).toBeGreaterThan(prevBox.x);
+  });
+});