avoid ambiguous term "relative sizing"; clarify width vs. height control classes

css.html

@@ -1540,9 +1540,9 @@ For example, <code>&lt;section&gt;</code> should be wrapped as inline.
 
 
     <h2 id="forms-control-sizes">Control sizing</h2>
-    <p>Use relative sizing classes like <code>.input-large</code> or match your inputs to the grid column sizes using <code>.col-lg-*</code> classes.</p>
+    <p>Set heights using classes like <code>.input-large</code>, and set widths using grid column classes like <code>.col-lg-*</code>.</p>
 
-    <h3>Relative sizing</h3>
+    <h3>Height sizing</h3>
     <p>Create larger or smaller form controls that match button sizes.</p>
     <form class="bs-example bs-example-control-sizing">
       <div class="controls docs-input-sizes">