Attempts to fix #8645: add code comments to grid example to clarify behavior

css.html

@@ -239,15 +239,20 @@ base_url: "../"
       </div>
     </div>
 {% highlight html %}
+<!-- Stack the columns on mobile by making one full-width and the other half-width -->
 <div class="row">
   <div class="col-12 col-lg-8">8</div>
   <div class="col-6 col-lg-4">4</div>
 </div>
+
+<!-- Columns start at 50% wide on mobile and bump up to 33.3% wide on desktop -->
 <div class="row">
   <div class="col-6 col-lg-4">4</div>
   <div class="col-6 col-lg-4">4</div>
   <div class="col-6 col-lg-4">4</div>
 </div>
+
+<!-- Columns are always 50% wide, on mobile and desktop -->
 <div class="row">
   <div class="col-6 col-lg-6">6</div>
   <div class="col-6 col-lg-6">6</div>