Less on 2 symbols

Merge branch 'borderless-table' of https://github.com/Varunram/bootstrap into Varunram-borderless-table

Opera 19 was released in January 2014 and auto-updates so I suggest no need to mention about browser support for this old version.

Removed '**Animated progress bars don't work in Opera 12**—as they don't support CSS3 animations.' note.

Bootstrap 4 doesn't (and doesn't need to) support the ancient Opera 12 released in 2012 with a 0.04% marketshare so no need to mention.

Convert them to 8-bit and compress them with optipng and zopflipng.

Before: 902 KB (923,969 bytes)
After:  431 KB (441,372 bytes)

* Prevent print utils from overriding all other display utils

Fixes #25221.

I agree with the referenced issue—this is unexpected and also causes a serious bug when mixed with other utility classes. This wasn't an issue in v3 given we had different utilities for hiding that weren't focused on display property.

* Add printing changes to migration docs

* unrelated heading sentence case change

* List out all .d-print- classes

When changing `$input-border-width`, `$input-height-border` does not change and `select.form-control` `custom-select` `custom-file` will still have `$input-height` which is resolved from `$input-btn-border-width`

This will work in cases when want controls with border, and buttons without.

Temporary fix will be to override 2 variables

```
$input-border-width: 2px !default;

// which is
// $input-height-border: $input-btn-border-width * 2 !default;
$input-height-border: $input-border-width * 2 !default;
```

* Add order-*-last grid class

* copy updates

Closes #25231

Merge branch 'form-check-input-validation' of https://github.com/supergibbs/bootstrap into supergibbs-form-check-input-validation

Closes https://github.com/twbs/bootstrap/issues/25316

* Update copyright range to include 2018

* Extend copyright date range on new files from 2017 to include 2018

* Make dropright snippet the same as demo

* Add missing .dropdown-toggle-split class

* Make clear the split button label the same as demo

* heading for better linking

* tell folks where to start

* more headings

* required keys section added, closes #25293