The division operator `/` from Sass is deprecated because `/` is used in
CSS for uses other than dividing numbers. That's why we were getting
many warnings like:
```
Deprecation Warning: Using / for division outside of calc() is
deprecated and will be removed in Dart Sass 2.0.0.
Recommendation: math.div($line-height, 2) or calc($line-height / 2)
More info and automated migrator: https://sass-lang.com/d/slash-div
margin-top: $line-height / 2;
```
Since using math.div makes the code harder to read and `calc` is
universally supported by all browsers (although the implementation in
Internet Explorer doesn't work in certain cases), we're using `calc`
when assigning the value to a CSS property.
However, we're also using divisions when assigning Sass variables, and
in those cases using `calc` is trickier because sometimes these
variables are used in other operations. We'll handle these cases in the
next commit.
This way we remove duplication and it'll be easier to add better support
for RTL languages.
In a few years this might not be necessary since support for the `gap`
property in a flexbox layout will improve. At the time of writing,
however, only 86.5% of the browsers support it [1].
[1] https://caniuse.com/flexbox-gap
As mentioned in commit 5214d89c8, there are several issues with
submitting a form when a `<select>` tag changes. In particular, keyboard
users might accidentally fire the event while browsing the options, and
screen reader users will find a form with no obvious way to submit it.
In this case, there's an extra problem: in commit be8a0dbe8 we added a
second `<select>` field to this form, which also submitted on change.
Sometimes users changed one of the values and wanted to change the other
value as well before submitting the form. However, it wasn't possible,
because we would submit it before they had a chance to change the second
value.
So now we don't submit the form on change and add a submit button. This
is similar to what we do in the "Advanced filters" we use in several
places.
