clarify style property naming in Dart

Added callout now that @vicb has clarified issues related to style
property naming.

Author: chalin

public/docs/dart/latest/guide/template-syntax.jade

@@ -58,6 +58,20 @@ block dart-class-binding-bug
 
       [6901]: http://github.com/angular/angular/issues/6901
 
+block style-property-name-dart-diff
+  .callout.is-helpful
+    header Dart difference: Style property names
+    :marked
+      While [camelCase](glossary.html#camelcase) and
+      [dash-case](glossary.html#dash-case) style property naming schemes are
+      equivalent in Angular Dart, only dash-case names are recognized by the
+      `dart:html` [CssStyleDeclaration][CssSD] methods `getPropertyValue()`
+      and `setProperty()`. Hence, we recommend only using dash-case for style
+      property names.
+      
+      [CssSD]: https://api.dartlang.org/stable/1.16.1/dart-html/CssStyleDeclaration-class.html
+
+
 block dart-no-truthy-falsey
   .callout.is-helpful
     header Dart difference: No truthy/falsey values

public/docs/ts/latest/guide/template-syntax.jade

@@ -687,7 +687,12 @@ block dart-class-binding-bug
 
 .l-sub-section
   :marked
-    Note that the _style property_ name can be written in camelCase, such as `fontSize`.
+    Note that a _style property_ name can be written in either
+    [dash-case](glossary.html#dash-case), as shown above, or
+    [camelCase](glossary.html#camelcase), such as `fontSize`.
+
+block style-property-name-dart-diff
+  //- N/A
 
 .l-main-section
 :marked