cr-dialog scrollbar should span entire body

ui/webui/resources/cr_elements/cr_dialog/cr_dialog.html

 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/assert.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html">
 
 <dom-module id="cr-dialog">
   <template>
     <style>
       :host {
         border: 0;
@@ skipping 39 matching lines @@
       .body-container {
         display: flex;
         flex-direction: column;
         max-width: 800px;
         min-width: 512px;
         /* TODO(dbeam): use <paper-dialog-scrollable> to get dividers? */
         overflow: auto;
       }
 
       :host ::content .body {
-        margin: 12px 0;
+        padding-bottom: 12px;
+        padding-top: 12px;
       }
 
       :host ::content .body,
       :host ::content .title {
         -webkit-padding-end: 24px;
         -webkit-padding-start: 24px;
         flex: 1;
       }
 
       :host ::content .button-container {
@@ skipping 24 matching lines @@
       </paper-icon-button>
     </div>
     <div class="body-container">
       <content select=".body"></content>
     </div>
     <content select=".button-container"></content>
     <content select=".footer"></content>
   </template>
   <script src="cr_dialog.js"></script>
 </dom-module>