DOMUI prefs: Remove use of tables for layout on the Under the Hood pane.

chrome/browser/resources/options/options_page.css

 #settings-title {
   height: 30px;
   -webkit-padding-end: 15px;
   padding-top: 20px;
   text-align: end;
   font-size: 140%;
   color: #c7c7c7;
 }
 
 #main-content {
@@ skipping 135 matching lines @@
   width: 150px;
   font-size: 75%;
   -webkit-padding-start: 15px;
   vertical-align: top;
 }
 
 .option {
   margin-top: 5px;
 }
 
-.option-control-table {
+.option-control-table, section > div:only-of-type {
   margin-top: 5px;
   -webkit-padding-start: 10px;
 }
 
 .suboption {
   -webkit-margin-start: 18px;
 }
 
+/* TODO(stuartmorgan): make this less specific once all pages
+ * are converted to the non-table style.
+ */
+section > div:only-of-type label {
+  display: block;
+}
+
 .hidden {
   display: none;
 }
 
 .touch-slider {
   -webkit-appearance: slider-horizontal;
 }
+
+input[type="checkbox"] {
+  margin-top: 6px;
+}