I noticed that in the mobile phone environment the class "mx-wrapped-input" disappears.
Hope that helps.
Did you try using a .mx-fileinput .mx-normal-form selector for your mobile styling?
If you get to try this, try to have a look at the styles present in the console and if the styles you put in come through in the front end. Don't really see why they wouldn't, might also be worth checking if your SASS compiled (if applicable) and if other CSS came through in you app instance.
Hope this helps
Thank you for your reply. I tried to add the selector.
But I can't change the background color of the button. Neither I can change the label on the button and the label 'No file chosen'.