Note that the sticky plugin no longer works with `data-top-anchor="0"`.
Quoting from the Foundation documentation:
> It's important to note that sticky requires a bit of developer input
> to work properly. (...) It's also important to set the minimum
> top-anchor point to 1px, otherwise it'll never stick!
Also note that the foundation-sites package already depends on the
motion-ui package, so we don't have to explicitly include this
dependency anymore. Since now we're using Dart Sass, we can upgrade to
motion-ui 2.0.5.
Since this new version already defines variables before using `!global`
with them, we can remove the changes we did in commit 1e1edc02e.
Finally, note we aren't removing the "upgrade Foundation" part of the
comment in `config/initializers/sass.rb` because we're still getting one
Dart Sass warning due to Foundation's code:
```
Deprecation Warning: Passing percentage units to the global abs()
function is deprecated.
In the future, this will emit a CSS abs() function to be by the
ser.
To preserve current behavior: math.abs(100%)
To emit a CSS abs() now: abs(#{100%})
$divisor: abs($divisor);
```
This warning will be removed when we upgrade to Foundation 6.8.1. We
aren't upgrading to that version now for the same reason we don't
upgrade two minor Rails versions at once: it would increase the chance
of breaking something.
The action and the views were almost identical, with the supports
progress and the HTML classes of the success message element being the
only exceptions; we can use CSS for the styles instead.
