[css-color-5][editorial] Add example with omitted colorspace, #10484

Author: svgeesus

css-color-5/Overview.bs

@@ -236,6 +236,16 @@ Mixing Colors: the ''color-mix()'' Function {#color-mix}
 If no color interpolation method is specified, assume Oklab.
 Otherwise, use the specified colorspace for mixing.
 
+<div class="example" id="ex-omitted-colorspace">
+	For example, these two are exactly equivalent:
+
+	<pre class="lang-css">
+		color-mix(in oklab, firebrick, goldenrod)
+		color-mix(firebrick, goldenrod)
+	</pre>
+
+</div>
+
 <h3 id="color-mix-percent-norm">
 	Percentage Normalization
 </h3>