Improves forms migration guide, docs, and scss (#24348)

* fixes migration forms guides

* removes container from Horizontal form

* adds col-form-label sizes on form docs

* removes .form-control-label from forms.scss

* add note to migration

1 files changed, 70 insertions, 45 deletions

diff --git a/docs/4.0/components/forms.md b/docs/4.0/components/forms.md
index ba5633850..84891d841 100644
--- a/docs/4.0/components/forms.md
+++ b/docs/4.0/components/forms.md
@@ -365,62 +365,87 @@ Create horizontal forms with the grid by adding the `.row` class to form groups
 Be sure to add `.col-form-label` to your `<label>`s as well so they're vertically centered with their associated form controls. For `<legend>` elements, you can use `.col-form-legend` to make them appear similar to regular `<label>` elements.
 
 {% example html %}
-<div class="container">
-  <form>
-    <div class="form-group row">
-      <label for="inputEmail3" class="col-sm-2 col-form-label">Email</label>
-      <div class="col-sm-10">
-        <input type="email" class="form-control" id="inputEmail3" placeholder="Email">
-      </div>
+<form>
+  <div class="form-group row">
+    <label for="inputEmail3" class="col-sm-2 col-form-label">Email</label>
+    <div class="col-sm-10">
+      <input type="email" class="form-control" id="inputEmail3" placeholder="Email">
     </div>
-    <div class="form-group row">
-      <label for="inputPassword3" class="col-sm-2 col-form-label">Password</label>
-      <div class="col-sm-10">
-        <input type="password" class="form-control" id="inputPassword3" placeholder="Password">
-      </div>
+  </div>
+  <div class="form-group row">
+    <label for="inputPassword3" class="col-sm-2 col-form-label">Password</label>
+    <div class="col-sm-10">
+      <input type="password" class="form-control" id="inputPassword3" placeholder="Password">
     </div>
-    <fieldset class="form-group">
-      <div class="row">
-        <legend class="col-form-legend col-sm-2">Radios</legend>
-        <div class="col-sm-10">
-          <div class="form-check">
-            <label class="form-check-label">
-              <input class="form-check-input" type="radio" name="gridRadios" id="gridRadios1" value="option1" checked>
-              Option one is this and that&mdash;be sure to include why it's great
-            </label>
-          </div>
-          <div class="form-check">
-            <label class="form-check-label">
-              <input class="form-check-input" type="radio" name="gridRadios" id="gridRadios2" value="option2">
-              Option two can be something else and selecting it will deselect option one
-            </label>
-          </div>
-          <div class="form-check disabled">
-            <label class="form-check-label">
-              <input class="form-check-input" type="radio" name="gridRadios" id="gridRadios3" value="option3" disabled>
-              Option three is disabled
-            </label>
-          </div>
-        </div>
-      </div>
-    </fieldset>
-    <div class="form-group row">
-      <div class="col-sm-2">Checkbox</div>
+  </div>
+  <fieldset class="form-group">
+    <div class="row">
+      <legend class="col-form-legend col-sm-2">Radios</legend>
       <div class="col-sm-10">
         <div class="form-check">
           <label class="form-check-label">
-            <input class="form-check-input" type="checkbox"> Check me out
+            <input class="form-check-input" type="radio" name="gridRadios" id="gridRadios1" value="option1" checked>
+            Option one is this and that&mdash;be sure to include why it's great
+          </label>
+        </div>
+        <div class="form-check">
+          <label class="form-check-label">
+            <input class="form-check-input" type="radio" name="gridRadios" id="gridRadios2" value="option2">
+            Option two can be something else and selecting it will deselect option one
+          </label>
+        </div>
+        <div class="form-check disabled">
+          <label class="form-check-label">
+            <input class="form-check-input" type="radio" name="gridRadios" id="gridRadios3" value="option3" disabled>
+            Option three is disabled
           </label>
         </div>
       </div>
     </div>
-    <div class="form-group row">
-      <div class="col-sm-10">
-        <button type="submit" class="btn btn-primary">Sign in</button>
+  </fieldset>
+  <div class="form-group row">
+    <div class="col-sm-2">Checkbox</div>
+    <div class="col-sm-10">
+      <div class="form-check">
+        <label class="form-check-label">
+          <input class="form-check-input" type="checkbox"> Check me out
+        </label>
       </div>
     </div>
-  </form>
-</div>
+  </div>
+  <div class="form-group row">
+    <div class="col-sm-10">
+      <button type="submit" class="btn btn-primary">Sign in</button>
+    </div>
+  </div>
+</form>
+{% endexample %}
+
+##### Horizontal form label sizing
+
+Be sure to use `.col-form-label-sm` or `.col-form-label-lg` to your `<label>`s to correctly follow the size of `.form-control-lg` and `.form-control-sm`.
+
+{% example html %}
+<form>
+  <div class="form-group row">
+    <label for="colFormLabelSm" class="col-sm-2 col-form-label col-form-label-sm">Email</label>
+    <div class="col-sm-10">
+      <input type="email" class="form-control form-control-sm" id="colFormLabelSm" placeholder="col-form-label-sm">
+    </div>
+  </div>
+  <div class="form-group row">
+    <label for="colFormLabel" class="col-sm-2 col-form-label">Email</label>
+    <div class="col-sm-10">
+      <input type="email" class="form-control" id="colFormLabel" placeholder="col-form-label">
+    </div>
+  </div>
+  <div class="form-group row">
+    <label for="colFormLabelLg" class="col-sm-2 col-form-label col-form-label-lg">Email</label>
+    <div class="col-sm-10">
+      <input type="email" class="form-control form-control-lg" id="colFormLabelLg" placeholder="col-form-label-lg">
+    </div>
+  </div>
+</form>
 {% endexample %}
 
 #### Column sizing