[css3-box] Added the idea to use float & float-offset for vertically

centering.

Author: bert-github

css-box/Overview.src.html

@@ -322,6 +322,22 @@ <h2 class="no-toc no-num">Status of this document</h2>
 
 	  <p>This cannot top-align the first child and bottom-align
 	    the second.
+
+	<li>
+	  <p>Vertically centering a single element could also be
+	    modeled as a float with an offset. A draft of
+	    [[CSS-PAGE-FLOATS]] from 2013 suggests the following to
+	    center a P vertically inside its parent DIV:
+
+	  <pre>DIV {height: 15em;
+  colums: 1}            /* Make the DIV act like a "page" */
+P {float: top left;     /* Place the P in the corner of the DIV... */
+  float-offset: 0 50%}  /* ... and add 50% offset vertically */</pre>
+
+	  <p>Floats like this also allow to put all children at the
+	    top and the last child against the bottom. But only one
+	    child: trying to push multiple children down to the bottom
+	    results in their order being reversed.
       </ol>
     </div>