[css-color-4] add example with multiple fallbacks

Author: svgeesus

css-color-4/Overview.bs

@@ -2434,6 +2434,14 @@ Profiled, Device-dependent Colors</h2>
 		the fallback color will be used.
 	</div>
 
+	<div class="example">
+		An intense green is provided in prophoto-rgb space.
+		It has a first fallback, which is the same color in display-p3
+		in case prophoto is unsupported. The color is in gamut of display-p3.
+		Lastly, a desaturated sRGB fallback is provided.
+		<pre class="lang-css">color(prophoto-rgb 0.4835 0.9167 0.2188, display-p3 0.3499 0.9800 0.1399, rgb(33.44% 96.68% 21.07%))/pre>
+	</div>
+
 <h3 id="predefined">
 Predefined colorspaces: ''srgb'', ''display-p3'', ''a98-rgb'', ''prophoto-rgb'', ''rec2020'',
 ''xyz'' and ''lab'''.</h3>