Specify `--source-map-contents true` for node-sass and `source-map-inline-sources` for clean-css.

Without this, the sourcemaps weren't found.

given `width: 100%` is always on a container now and it's constrained by max-width, we can remove our navbar changes from #21722 and #22383

The "aria-controls" attribute must point to an element in the same document.

~30% savings.

Before: 374 KB (383.630 bytes)
After:  304 KB (311.505 bytes)

Ignore ESLint error in ie-emulation-modes-warning.js.

Although the error is valid, enough time has been spent on old IE's problems, so just ignore it.

Remove https://bugzilla.mozilla.org/show_bug.cgi?id=1282363
because CSSWG deemed Firefox's behavior to be the correct behavior per
https://github.com/w3c/csswg-drafts/issues/314

Replace it with a Chrome bug about changing Chrome to follow the spec & Firefox:
https://bugs.chromium.org/p/chromium/issues/detail?id=269061

* https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/817822/
* https://bugs.chromium.org/p/chromium/issues/detail?id=465274
* https://bugs.chromium.org/p/chromium/issues/detail?id=510079
* https://bugs.webkit.org/show_bug.cgi?id=158276

The transitioncancel event was shipped in Firefox 53 
https://bugzilla.mozilla.org/show_bug.cgi?id=1264125

(#22414) Rename for consistency `$custom-checkbox-border-radius`, `$custom-checkbox-icon-checked`, `$custom-checkbox-indeterminate-bg`, `$custom-checkbox-icon-indeterminate`, `$custom-checkbox-indeterminate-box-shadow`, `$custom-radio-border-radius`, `$custom-radio-icon-checked` to `$custom-checkbox-indicator-border-radius`, `$custom-checkbox-indicator-icon-checked`, `$custom-checkbox-indicator-indeterminate-bg`, `$custom-checkbox-indicator-icon-indeterminate`, `$custom-checkbox-indicator-indeterminate-box-shadow`, `$custom-radio-indicator-border-radius`, `$custom-radio-indicator-icon-checked`, respectively

fix location of favicons so it loads when viewing the examples. This is the only one I found in the project, so I am assuming it is the right one to point to (#22895)