scope th bottom vertical-align to only thead, update code styles to include more comments in less file and scrollable option for pre tag

less/code.less

@@ -11,12 +11,16 @@ pre {
   color: @grayDark;
   .border-radius(3px);
 }
+
+// Inline code
 code {
   padding: 3px 4px;
   color: #d14;
   background-color: #f7f7f9;
   border: 1px solid #e1e1e8;
 }
+
+// Blocks of code
 pre {
   display: block;
   padding: (@baseLineHeight - 1) / 2;
@@ -44,3 +48,9 @@ pre {
     border: 0;
   }
 }
+
+// Enable scrollable blocks of code
+.pre-scrollable {
+  max-height: 340px;
+  overflow-y: scroll;
+}