Adjusting the height of the header widget

Hello, I have implemented the header widget on my site. I am using a search box plugin in that widget. It looks good on desktop. https://www.mailboxesbybathx.com/

However on mobile devices, the widget seems to make the search box really thin (not tall) you cant even see the search button magnifying glass. Is there a way to adjust the height of the search box (widget height) only on mobile devices (tablets, and smart phones)?

Or is this a plugin issue?

http://www.responsinator.com/?url=www.mailboxesbybathx.com

Thanks!