v5: Forms update (#28450)

* Initial spike of consolidated form checks

* Stub out forms rearrangement

- Prepping to drop non-custom file and range inputs
- Prepping to merge custom and native checks and radios (with switches)
- Prepping to merge custom select with form select
- Moving docs arround so forms has it's own area given volume of CSS

* Move input group Sass file to forms subdir

* Start to split and move the docs around

* Simpler imports

* Copyediting

* delete overview file

* Remove commented out code

* remove the custom-forms import

* rewrite flex-check as form-check, replace all custom properties

* Remove old forms doc

* stub out new subpage link section

* update migration guide

* Update nav, forms overview in page nav, and descriptions

* fix check bg position

* fix margin-top calculation

* rename .custom-select to .form-select

* Update validation styles for new checks

* add some vertical margin, fix inline checks

* fix docs examples

* better way to do this contents stuff, redo the toc while i'm at it

* page restyle for docs while here

* un-callout that, edit text

* redo padding on toc

* fix toc

* start to cleanup checks docs

* Rewrite Markdown tables into HTML

* Redesign tables, redo their docs

* Replace Open Iconic icons with custom Bootstrap icons

* Redesign the docs navbar, add a subheader, redo the sidebar

* Redesign docs homepage a bit

* Simplify table style overrides for docs tables

* Simplify docs typography for page titles and reading line length

* Stub out icons page

* Part of sidebar update, remove migration from nav.yml

* Move toc CSS to separate partial

* Change appearance of overview page

* fix sidebar arrow direction

* Add footer to docs layout

* Update descriptions

* Drop the .form-group class for margin utilities

* Remove lingering form-group-margin-bottom var

* improve footer spacing

* add headings to range page

* uncomment form range css

* Rename .custom-range to .form-range

* Drop unused docs var

* Uncomment the comment

* Remove unused variable

* Fix radio image sizing

* Reboot update: reset horizontal ul and ol padding

* de-dupe IDs

* tweak toc styles

* nvm, fix dropdown versions stuff

* remove sidebar nav toggle for now

* broken html

* fix more broken html, move css

* scss linting

* comment out broken helper docs

* scope styles

* scope styles

* Fixes #25540 and fixes #26407 for v5 only

* Update sidebar once more

* Match new sidenav order

* fix syntax error

* Rename custom-file to form-file, update paths, update migration docs for previous changes in #28696

* rename back

* fix size and alignment

* rename that back too

1 files changed, 188 insertions, 0 deletions

diff --git a/scss/forms/_input-group.scss b/scss/forms/_input-group.scss
new file mode 100644
index 000000000..099accecb
--- /dev/null
+++ b/scss/forms/_input-group.scss
@@ -0,0 +1,188 @@
+// stylelint-disable selector-no-qualifying-type
+
+//
+// Base styles
+//
+
+.input-group {
+  position: relative;
+  display: flex;
+  flex-wrap: wrap; // For form validation feedback
+  align-items: stretch;
+  width: 100%;
+
+  > .form-control,
+  > .form-select,
+  > .form-file {
+    position: relative; // For focus state's z-index
+    flex: 1 1 0%;
+    margin-bottom: 0;
+
+    + .form-control,
+    + .form-select,
+    + .form-file {
+      margin-left: -$input-border-width;
+    }
+  }
+
+  // Bring the "active" form control to the top of surrounding elements
+  > .form-control:focus,
+  > .form-select:focus,
+  > .form-file .form-file-input:focus ~ .form-file-label {
+    z-index: 3;
+  }
+
+  // Bring the custom file input above the label
+  > .form-file .form-file-input:focus {
+    z-index: 4;
+  }
+
+  > .form-control,
+  > .form-select {
+    &:not(:last-child) { @include border-right-radius(0); }
+    &:not(:first-child) { @include border-left-radius(0); }
+  }
+
+  // Custom file inputs have more complex markup, thus requiring different
+  // border-radius overrides.
+  > .form-file {
+    display: flex;
+    align-items: center;
+
+    &:not(:last-child) .form-file-label { @include border-right-radius(0); }
+    &:not(:first-child) .form-file-label { @include border-left-radius(0); }
+  }
+}
+
+
+// Prepend and append
+//
+// While it requires one extra layer of HTML for each, dedicated prepend and
+// append elements allow us to 1) be less clever, 2) simplify our selectors, and
+// 3) support HTML5 form validation.
+
+.input-group-prepend,
+.input-group-append {
+  display: flex;
+
+  // Ensure buttons are always above inputs for more visually pleasing borders.
+  // This isn't needed for `.input-group-text` since it shares the same border-color
+  // as our inputs.
+  .btn {
+    position: relative;
+    z-index: 2;
+
+    &:focus {
+      z-index: 3;
+    }
+  }
+
+  .btn + .btn,
+  .btn + .input-group-text,
+  .input-group-text + .input-group-text,
+  .input-group-text + .btn {
+    margin-left: -$input-border-width;
+  }
+}
+
+.input-group-prepend { margin-right: -$input-border-width; }
+.input-group-append { margin-left: -$input-border-width; }
+
+
+// Textual addons
+//
+// Serves as a catch-all element for any text or radio/checkbox input you wish
+// to prepend or append to an input.
+
+.input-group-text {
+  display: flex;
+  align-items: center;
+  padding: $input-padding-y $input-padding-x;
+  margin-bottom: 0; // Allow use of <label> elements by overriding our default margin-bottom
+  @include font-size($input-font-size); // Match inputs
+  font-weight: $font-weight-normal;
+  line-height: $input-line-height;
+  color: $input-group-addon-color;
+  text-align: center;
+  white-space: nowrap;
+  background-color: $input-group-addon-bg;
+  border: $input-border-width solid $input-group-addon-border-color;
+  @include border-radius($input-border-radius);
+
+  // Nuke default margins from checkboxes and radios to vertically center within.
+  input[type="radio"],
+  input[type="checkbox"] {
+    margin-top: 0;
+  }
+}
+
+
+// Sizing
+//
+// Remix the default form control sizing classes into new ones for easier
+// manipulation.
+
+.input-group-lg > .form-control:not(textarea),
+.input-group-lg > .form-select {
+  height: $input-height-lg;
+}
+
+.input-group-lg > .form-control,
+.input-group-lg > .form-select,
+.input-group-lg > .input-group-prepend > .input-group-text,
+.input-group-lg > .input-group-append > .input-group-text,
+.input-group-lg > .input-group-prepend > .btn,
+.input-group-lg > .input-group-append > .btn {
+  padding: $input-padding-y-lg $input-padding-x-lg;
+  @include font-size($input-font-size-lg);
+  line-height: $input-line-height-lg;
+  @include border-radius($input-border-radius-lg);
+}
+
+.input-group-sm > .form-control:not(textarea),
+.input-group-sm > .form-select {
+  height: $input-height-sm;
+}
+
+.input-group-sm > .form-control,
+.input-group-sm > .form-select,
+.input-group-sm > .input-group-prepend > .input-group-text,
+.input-group-sm > .input-group-append > .input-group-text,
+.input-group-sm > .input-group-prepend > .btn,
+.input-group-sm > .input-group-append > .btn {
+  padding: $input-padding-y-sm $input-padding-x-sm;
+  @include font-size($input-font-size-sm);
+  line-height: $input-line-height-sm;
+  @include border-radius($input-border-radius-sm);
+}
+
+.input-group-lg > .form-select,
+.input-group-sm > .form-select {
+  padding-right: $form-select-padding-x + $form-select-indicator-padding;
+}
+
+
+// Prepend and append rounded corners
+//
+// These rulesets must come after the sizing ones to properly override sm and lg
+// border-radius values when extending. They're more specific than we'd like
+// with the `.input-group >` part, but without it, we cannot override the sizing.
+
+
+.input-group > .input-group-prepend > .btn,
+.input-group > .input-group-prepend > .input-group-text,
+.input-group > .input-group-append:not(:last-child) > .btn,
+.input-group > .input-group-append:not(:last-child) > .input-group-text,
+.input-group > .input-group-append:last-child > .btn:not(:last-child):not(.dropdown-toggle),
+.input-group > .input-group-append:last-child > .input-group-text:not(:last-child) {
+  @include border-right-radius(0);
+}
+
+.input-group > .input-group-append > .btn,
+.input-group > .input-group-append > .input-group-text,
+.input-group > .input-group-prepend:not(:first-child) > .btn,
+.input-group > .input-group-prepend:not(:first-child) > .input-group-text,
+.input-group > .input-group-prepend:first-child > .btn:not(:first-child),
+.input-group > .input-group-prepend:first-child > .input-group-text:not(:first-child) {
+  @include border-left-radius(0);
+}