Prevent horizontal scrolling

Low-vision users who cannot read at standard zoom levels increase browser zoom to 200–400%. At these zoom levels, a 1280px-wide page becomes effectively 320px wide. If elements overflow the viewport, users must scroll both vertically and horizontally to read content — this is exhausting and error-prone with a screen magnifier. WCAG 2.1 SC 1.4.10 (Reflow) specifically addresses this, requiring that all content is available without two-dimensional scrolling at 400% zoom.

Quick Reference

• Pages must not produce horizontal scrollbars at viewport widths of 320px and above — WCAG 2.1 SC 1.4.10 (Reflow)
• WCAG 2.1 SC 1.4.10 requires content to reflow at 400% zoom (equivalent to 320px CSS width) without horizontal scroll
• Common causes: fixed-width elements wider than the viewport, width: 100vw not accounting for scrollbar width, long unbreakable strings, white-space: nowrap
• Use max-width: 100% on images and media, overflow-wrap: break-word on text containers, and fluid layout units

Check

Test the page at a 320px CSS viewport width (equivalent to 400% browser zoom on a 1280px screen). Look for horizontal scrollbars or content overflowing outside the viewport. Specifically check: (1) elements with fixed width values in px that exceed the viewport; (2) min-width values that prevent shrinking; (3) images or media without max-width: 100%; (4) white-space: nowrap on text that causes overflow; (5) width: 100vw on elements (scrollbar width causes overflow); (6) long URLs or unbreakable strings in content areas.

Fix

(1) Replace fixed width: Npx on layout containers with max-width: Npx plus width: 100%. (2) Add max-width: 100% and height: auto to all images and media. (3) Apply overflow-wrap: break-word (with fallback word-wrap: break-word) to text containers that may contain long strings. (4) Replace width: 100vw with width: 100% on full-width elements (avoid scrollbar overflow). (5) Use CSS Grid or Flexbox with flex-wrap: wrap for multi-column layouts. (6) For data tables, wrap in a scrollable container: overflow-x: auto on the table wrapper, not the page body.