Base: Add inline properties to custom-properties test page

Base/res/html/misc/custom-properties.html

@@ -152,6 +152,14 @@
         This should be cyan
     </div>
 
+    <h2>Inline properties</h2>
+    <pre>
+        &lt;div style="--color: turquoise; background-color: var(--color)"&gt;
+    </pre>
+    <div class="box" style="--color: turquoise; background-color: var(--color)">
+        This should be turquoise
+    </div>
+
     <h2>Nested var()</h2>
     <pre>
         :root {