Prefer leading zeros in CSS values

This was reversed in the internal style guide a while ago to align the guidance with our autoformatting tooling configuration.

Any optimisations to reduce file size should be handled by compilers and minifiers.

htmlcssguide.html

@@ -592,11 +592,11 @@ <h4 id="0_and_Units" class="numbered">0 and Units</h4>
 
 <h4 id="Leading_0s" class="numbered">Leading 0s</h4>
 
-<p>Omit leading “0”s in values.</p>
+<p>Always include leading “0”s in values.</p>
 
-<p>Do not put <code>0</code>s in front of values or lengths between -1 and 1.</p>
+<p>Put <code>0</code>s in front of values or lengths between -1 and 1.</p>
 
-<pre><code class="language-css good">font-size: .8em;
+<pre><code class="language-css good">font-size: 0.8em;
 </code></pre>
 
 <h4 id="Hexadecimal_Notation" class="numbered">Hexadecimal Notation</h4>