Add missing placeholders and <select> in Grid sizing code snippet

docs/base-css.html

@@ -1225,9 +1225,18 @@ For example, <code>section</code> should be wrapped as inline.
             </div>
           </form>
 <pre class="prettyprint linenums">
-&lt;input class="span1" type="text"&gt;
-&lt;input class="span2" type="text"&gt;
-&lt;input class="span3" type="text"&gt;
+&lt;input class="span1" type="text" placeholder=".span1"&gt;
+&lt;input class="span2" type="text" placeholder=".span2"&gt;
+&lt;input class="span3" type="text" placeholder=".span3"&gt;
+&lt;select class="span1"&gt;
+  ...
+&lt;/select&gt;
+&lt;select class="span2"&gt;
+  ...
+&lt;/select&gt;
+&lt;select class="span3"&gt;
+  ...
+&lt;/select&gt;
 </pre>
 
           <p>For multiple grid inputs per line, <strong>use the <code>.controls-row</code> modifier class for proper spacing</strong>. It floats the inputs to collapse white-space, sets the proper margins, and the clears the float.</p>

docs/templates/pages/base-css.mustache

@@ -1162,9 +1162,18 @@
             </div>
           </form>
 <pre class="prettyprint linenums">
-&lt;input class="span1" type="text"&gt;
-&lt;input class="span2" type="text"&gt;
-&lt;input class="span3" type="text"&gt;
+&lt;input class="span1" type="text" placeholder=".span1"&gt;
+&lt;input class="span2" type="text" placeholder=".span2"&gt;
+&lt;input class="span3" type="text" placeholder=".span3"&gt;
+&lt;select class="span1"&gt;
+  ...
+&lt;/select&gt;
+&lt;select class="span2"&gt;
+  ...
+&lt;/select&gt;
+&lt;select class="span3"&gt;
+  ...
+&lt;/select&gt;
 </pre>
 
           <p>{{_i}}For multiple grid inputs per line, <strong>use the <code>.controls-row</code> modifier class for proper spacing</strong>. It floats the inputs to collapse white-space, sets the proper margins, and the clears the float.{{/i}}</p>