The browser will zoom if the font-size is less than 16px and the default font-size for form elements is 11px (at least in Chrome and Safari).
来源：https://stackoverflow.com/questions/2989263/disable-auto-zoom-in-input-text-tag-safari-on-iphone 回答1
也就是页面上input默认字体大小是11px，当页面上字体大小小于16px时，点击，页面会自动放大。
->设置页面上所需控制的控件字体大小不小于16px