Test zoom at 200%.
WCAG: https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-scale.html

Testing

The W3C Web Content Accessibility Guidelines defines 200% as the minimum zoom level below which all content should still be readable. Testing your web page or application with 200% zoom is easiest in Firefox. Here’s how:

1. Turning on text-only zoom (View > Zoom > Zoom Text Only).
2. Zoom in six times using Command + (Mac) or Control + (Windows).
3. Explore the page to be sure all content is readable. Watch especially for content that disappears beyond the margins of its container or overlaps with other text.

4. NOTE:
   By default, the enlargement options are: (start by doing ctrl+0 to start at 100%)

• 1.1 => 110%
• 1.2 => 120%
• 1.33 => 133%
• 1.5 => 150%
• 1.7 => 170%
• 2 => 200%
• 2.4 => 240%
• 3 => 300%

When using a desktop or notebook-based browser, you can also resize the window to simulate viewing on a small screen.
Basic functionality should not be broken.

• Verify text is readable
• Verify that content does not disappear beyond margins of container
• Verify content does not overlap other text