This commit should fix the issue with the search input zoom in iOS: https://github.com/discourse/discourse/commit/a452933071b9ad844b02217619aea1a864a02978
The intended behaviour is to enable zooming on touch devices, but iOS automatically zooms on inputs with font size set to less than 16px, which is not a very fun experience, so we’ve implemented a workaround to avoid that auto-zoom.