In units of px, rem, em, how small can margin: be without causing mobile usability issues?

In units of pt, rem-calc, percent, em, how small can font-size: be without causing mobile usability issues?

The exact values can depend on the specific design and layout of your website, but here are some general guidelines:

Margin: For clickable elements, a minimum margin of 8px (or 0.5rem / 0.5em) is often recommended to ensure that elements are not too close together on mobile devices. However, the appropriate margin can depend on the size of the clickable elements themselves and the overall layout of your page.

Font-size: The minimum recommended font-size for body text on a mobile website is typically 16px (or 1rem / 1em / 12pt / 100%). For smaller text, such as captions or footnotes, a minimum of 12px (or 0.75rem / 0.75em / 9pt / 75%) is often recommended. However, the appropriate font-size can depend on the font family used and the user’s device and settings.

Remember, these are just guidelines and the actual values can depend on many factors. It’s always a good idea to test your website on various devices and screen sizes to ensure usability.