Some browsers on mobile, especially Apple ones, tend to autoscale the viewport. Autoscale happens when you click on the Input or the Text area if your inputs have font-size less than 16px. It’s painful for users to fill in such form as it scales while you type and doesn't scale back after a user stops typing.

To make all text elements on a page readable and legible without zooming, disable scaling by using this itty-bitty code snippet:

<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no" />

Want to go deeper and prevent scale effect only on input click? Check article on dynamo6 as well.