I can't see fieldset borders of Ext Js based web apps on iPad with any browser

Please be kind to view this fiddle https://fiddle.sencha.com/#fiddle/np9.

Please press the green play button and see the difference between viewing this on your Mac and using your iPad.

On your computer you'll see a frame around the button. It's the frame of the fieldset.

However, only recently, iPads don't show borders of fieldset componenets of Ext Js base web apps.

Why so?

Thank you