We're starting to use buttons instead of submit inputs where possible
because buttons are easier to style; for instance, buttons allow
pseudoelements. Rails has also changed the `button_to` helper to always
generate a <button> tag in recent versions [1].
In this case, buttons get on better with flex layouts, since by default
some browsers display submit inputs with `white-space: pre`, meaning
some of the text isn't visible on small screens.
[1] See pull request 40747 in https://github.com/rails/rails
8ec77723ed