Fixes #11436: mention in docs that .container isn't nestable; update docs to...

Fixes #11436: mention in docs that .container isn't nestable; update docs to mention width, not max-width

css.html

@@ -54,7 +54,8 @@ base_url: "../"
     <p>For improved cross-browser rendering, we use <a href="http://necolas.github.io/normalize.css/" target="_blank">Normalize</a>, a project by <a href="http://twitter.com/necolas" target="_blank">Nicolas Gallagher</a> and <a href="http://twitter.com/jon_neal" target="_blank">Jonathan Neal</a>.</p>
 
     <h3 id="overview-container">Containers</h3>
-    <p>Easily center a page's contents by wrapping its contents in a <code>.container</code>. Containers set <code>max-width</code> at various media query breakpoints to match our grid system.</p>
+    <p>Easily center a page's contents by wrapping its contents in a <code>.container</code>. Containers set <code>width</code> at various media query breakpoints to match our grid system.</p>
+    <p>Note that, due to <code>padding</code> and fixed widths, containers are not nestable by default.</p>
 {% highlight html %}
 <div class="container">
   ...