Should Back button close modal?
When the modal dialog is open, pressing the back button closes it. On a multi-step modal dialog, the back button can even navigate backwards through the steps! On most web apps, pressing the back button while a modal dialog is open will navigate to the previous page, rather than closing the modal.
Where should back button be placed?
Place a persistent Back to Top button in the lower right side of the page. This is where people expect to see it. This position is out of the way, but noticeable. When the button is placed in a different place on the screen, it is often ignored.
Are modals good web design?
Modals are disruptive by design. They tend to appear unexpectedly in the flow of the browsing experience, and always shift focus away from their parent window. This is a high cost for the user, so modals should always assist the user in their goals, not obstruct them.