docs($anchorScroll): fix example controller and style

Changed controller name in example html to ScrollCtrl to match name in example js.
Add styling to example html so scrollable area is not obtrusive to documentation page design.

Closes angular#3898

Author: benlesh

src/ng/anchorScroll.js

@@ -16,7 +16,7 @@
  * @example
    <example>
      <file name="index.html">
-       <div ng-controller="MainCtrl">
+       <div id="scrollArea" ng-controller="ScrollCtrl">
          <a ng-click="gotoBottom()">Go to bottom</a>
          <a id="bottom"></a> You're at the bottom!
        </div>
@@ -34,6 +34,11 @@
        }
      </file>
      <file name="style.css">
+       #scrollArea {
+         height: 350px;
+         overflow: auto;
+       }
+
        #bottom {
          display: block;
          margin-top: 2000px;