This was a great “Today I Learned” for me from Josh W. Comeau. If the
font-size of an
<input> is 16px or larger, Safari on iOS will focus into the input normally. But as soon as the
font-size is 15px or less, the viewport will zoom into that input. Presumably, because it considers that type too small and wants you to see what you are doing. So it zooms in to help you. Accessibility. If you don’t want that, make the font big enough.
Here’s Josh’s exact Pen if you want to have a play yourself.
In general, I’d say I like this feature. It helps people see what they are doing and discourages super-tiny font sizes. What is a slight bummer — and I really don’t blame anyone here — is that not all typefaces are created equal in terms of readability at different sizes. For example, here’s San Francisco versus Caveat at 16px.
You can view that example in Debug Mode to see for yourself and change the font size to see what does and doesn’t zoom.