[css-color-5] add LCH complement example

Author: svgeesus

css-color-5/Overview.bs

@@ -6,7 +6,7 @@ Status: ED
 Group: csswg
 TR: https://www.w3.org/TR/css-color-5/
 ED: https://drafts.csswg.org/css-color-5/
-Prevous Version: https://www.w3.org/TR/2020/WD-css-color-5-20200303/
+Previous Version: https://www.w3.org/TR/2020/WD-css-color-5-20200303/
 Work Status: exploring
 !Delta Spec: yes
 Editor: Chris Lilley, W3C, chris@w3.org, w3cid 1438
@@ -583,6 +583,15 @@ When an origin color is present, the following keywords can also be used in this
 	The result is <span class="swatch" style="--color: rgb(57.58% 32.47% 3.82%)"> </span> lch(49.80256% 54.0114 63.6769)
 </div>
 
+<div class="example">
+	This adds 180 degrees to the hue angle, giving the complementary color.
+	<pre>
+		--accent: <span class="swatch" style="--color: lightseagreen"></span> lightseagreen;
+		--complement:  <span class="swatch" style="--color: rgb(88.2814% 51.1047% 58.3039%"></span> LCH(from var(--accent) l c calc(h+180));
+	</pre>
+	lightseagreen is LCH(65.4937% 39.4484 190.1013), so --complement is <span class="swatch" style="--color: rgb(88.2814% 51.1047% 58.3039%)"></span> LCH(65.4937% 39.4484 370.1013)
+</div>
+
 <div class="example">
 	Fully desaturating a color to gray, keeping the exact same lightness: