Responsive automatic column resets weren't working because they inherited their `max-width` from lower grid tiers. This was because we were resetting the `width`, not the `max-width`.
The premise for #22376 was that if we removed the `max-width` and `flex` properties, we could use the column classes as `width` utilities. The problem that I didn't remember at the time is that column classes have horizontal `padding` on them. This doesn't work for setting `width`. Perhaps more importantly, this causes #22649—the automatic sizing of columns is broken with the absence of `flex` styles.
/cc @sachinsinghi
— Previously we weren't including the border-width on the computed height, leading to alignment issues.
— New system utilizes three variables (not ideal, but straightforward) for computing these heights. One for the vertical border, one for the line-height/font-size/padding dance, and one to add those together.
— Updates CSS across forms and custom forms to use new sizing. Special note here: form validation icon sizing uses the inner variables because background-image doesn't bleed into borders unless explicit background-clip.
* Replace backdrop with simple noop mouse listener
As discussed in https://github.com/twbs/bootstrap/pull/22422 the current
approach of injecting a backdrop (to work around iOS' broken event
delegation for the `click` event) has annoying consequences on
touch-enabled laptop/desktop devices.
Instead of a backdrop `<div>`, here we simply add extra empty/noop
mouse listeners to the immediate children of `<body>` (and remove
them when the dropdown is closed) in order to force iOS to properly
bubble a `click` resulting from a tap (essentially, method 2 from
https://www.quirksmode.org/blog/archives/2014/02/mouse_event_bub.html)
This is sufficient (except in rare cases where the user does manage to tap
on the body itself, rather than any child elements of body - which is not
very likely in an iOS phone/tablet scenario for most layouts) to get iOS to
get a grip and do the correct event bubbling/delegation, meaning the regular
"click" event will bubble back to the `<body>` when tapping outside of the dropdown,
and the dropdown will close properly (just like it already does, even without
this fix, in non-iOS touchscreen devices/browsers, like Chrome/Android and
Windows on a touch laptop).
This approach, though a bit hacky, has no impact on the DOM structure, and
has no unforeseen side effects on touch-enabled laptops/desktops. And crucially,
it works just fine in iOS.
* Remove dropdown backdrop styles
* Update doc for dropdowns and touch-enabled devices
