Implement tabs in mobile view

- Current behaviour: The output box is below the input box in the mobile view. (This requires the user to scroll a lot and in some mobile screens the output box is not visible without scrolling, which confuses the user and scrolling is not intuitive in such cases.)
- Required behaviour: There should be a tab UI to switch between the input and output boxes. (I'm open to suggestions on how the exact UI should look.)

Credits: @anuraghazra

Start by locating the mobile-view components that render the input and output boxes, then review the existing responsive UI. Done means mobile users can switch between input and output through tabs without excessive scrolling, with the tab appearance and behavior agreed upon.

Written by the indexing model from the issue text.