[css-conditional-3] Fix bikeshed <var>-related warnings.

This fixes the bikeshed warnings:
    The following <var>s were only used once in the document:
      'property'
      'value'
      'value', in algorithm 'supports(property, value)'
      'document.querySelector("a|b")'
    If these are not typos, please add an ignore='' attribute to the <var>.
    Successfully generated, with warnings

Mostly it does so by expanding the <div algorithm=""></div> elements to
include the entire algorithm, but also converts one <var> to a <code>
(which it should have been).

Author: dbaron

css-conditional-3/Overview.bs

@@ -643,10 +643,10 @@ partial namespace CSS {
 	<dt><code>supports(CSSOMString property, CSSOMString value)</code>, returns <code>boolean</code>
 	<dt><code>supports(CSSOMString conditionText)</code>, returns <code>boolean</code>
 	<dd>
+    <div algorithm="supports(property, value)">
 		When the {{supports(property, value)}} method is invoked
 		with two arguments <var>property</var> and <var>value</var>:
 
-    <div algorithm="supports(property, value)">
       1. If |property| is an [=ASCII case-insensitive=] match
         for any defined CSS property that the UA supports,
         and |value| successfully [=CSS/parses=] according to that property's grammar,
@@ -660,10 +660,10 @@ partial namespace CSS {
       as " width" isn't the name of any property due to the leading space.
     </div>
 
+    <div algorithm="supports(conditionText)">
 		When the {{supports(conditionText)}} method is invoked
     with a single <var>conditionText</var> argument:
 
-    <div algorithm="supports(conditionText)">
       1. If |conditionText|,
         [=CSS/parsed=] and evaluated as a <<supports-condition>>,
         would return true,
@@ -676,11 +676,11 @@ partial namespace CSS {
         return <code>true</code>.
       3. Otherwise, return <code>false</code>.
 
-    </div>
 
     All namespaces in the <var>conditionText</var> argument
     are considered invalid,
-    just as they are in <var>document.querySelector("a|b")</var>.
+    just as they are in <code>document.querySelector("a|b")</code>.
+    </div>
 </dl>
 
 <h2 class=no-num id=priv-sec>Privacy and Security Considerations</h2>