Add example for ui-sans-serif

Author: litherum

css-fonts-4/Overview.bs

@@ -427,21 +427,20 @@ Standard font families</h4>
                     <img alt="sample ui-serif font" src="images/ui-serif.png" >
                     <figcaption>Sample ui-serif font on macOS Catalina and iOS 13: New York</figcaption>
                 </figure>
-			</div>
+            </div>
 
-		<dt id="ui-sans-serif-def"><dfn>ui-sans-serif</dfn>
-			<dd>
-				This font family is used for the sans-serif variant of the system's
-				user interface. The purpose of ''ui-sans-serif'' is to allow web
-				content to integrate with the look and feel of the native OS.
+        <dt id="ui-sans-serif-def"><dfn>ui-sans-serif</dfn>
+        <dd>
+            This font family is used for the sans-serif variant of the system's
+            user interface. The purpose of ''ui-sans-serif'' is to allow web
+            content to integrate with the look and feel of the native OS.
 
-				<!-- TOD add sample
-					<div class="example">
-					<figure>
-						<img alt="sample ui-serif font" src="images/ui-serif.png" >
-						<figcaption>Sample ui-serif font on macOS Catalina and iOS 13: New York</figcaption>
-					</figure>
-				</div> -->
+            <div class="example">
+                <figure>
+                    <img alt="sample ui-sans-serif font" src="images/ui-sans-serif.png" >
+                    <figcaption>Sample ui-sans-serif font on macOS Catalina and iOS 13: San Francisco</figcaption>
+                </figure>
+            </div>
 
         <dt id="ui-monospace-def"><dfn>ui-monospace</dfn>
         <dd>