How can I change the layout for the first and last name fields so that they are placed one on top of another, instead of one being next to another? The same thing is needed for "city" and "state/province" fields. The reason I need this is that in my russian magento, in mobile view those entry fields overlap each other which confuses the user. Thanks
To change design of billing address and shipping address, you have to customize phtml file as per your design.
The first name and last name field are coming from template\persistent\checkout\onepage\billing.phtml and this phtml file called from template\checkout\onepage\billing.phtml.
By this two files you can adjust your billing and shipping address design.
This may help you.Thanks