Cleanup some classnames to match style.

chrome/browser/resources/net_internals/export_view.html

 <style>
 
 .export-view-explanation-warning {
   border: 2px solid red;
 }
 
 #export-view-privacy-warning {
   padding: 5px;
   color: red;
   border: 1px solid red;
 }
 
+#export-view-save-log-file {
+  font-size: 100%;
+  font-weight: bold;
+}
+
 </style>
 
-<div id=export-view-tab-content>
+<div id=export-view-tab-content class=content-box>
 
   <h2>Dump data</h2>
   <div style="margin: 8px">
     <p><input id=export-view-security-stripping-checkbox type=checkbox checked=yes>
        <label id=export-view-security-stripping-checkbox>
          Strip private information (cookies and credentials).
        </label>
        <div id=export-view-privacy-warning style="display:none">
          <b>WARNING</b>: Events were captured while full byte logging was enabled.
          This means the dump may contain private information.
        </div>
     </p>
     <textarea cols=50 rows=5 placeholder="Explain what went wrong here. (These notes will be included in the dump file. Be sure to mention the specific URLs, so investigators know what to look for!)" id=export-view-user-comments></textarea>
     <div>
-      <button id=export-view-save-log-file class=bigButton>Dump to file</button>
+      <button id=export-view-save-log-file>Dump to file</button>
     </div>
     <pre id=export-view-save-status-text></pre>
 
     <ul>
       <li><b>IMPORTANT</b>: First reproduce the problem while in recording mode.</li>
     </ul>
     <p>
       For more information see: 
       <a href="chrome://net-internals/help.html" target="_blank">
         How to get data for bug reports?
       </a>
     </p>
   </div>
 
   <iframe style="display: none" id=export-view-download-iframe></iframe>
 
 </div>