[css-color-4] clarify cylindrical, not spherical

Author: svgeesus

css-color-4/Overview.bs

@@ -1893,7 +1893,8 @@ Device-independent Colors: Lab and LCH</h2>
 	and is easy to calculate as it is a simple matrix multiplication.
 
 	LCH has the same L axis as Lab,
-	but uses polar coordinates C (chroma) and H (hue).
+	but uses polar coordinates C (chroma) and H (hue),
+	making it a polar, cylindrical coordinate system.
 	C is the geometric distance from the L axis
 	and H is the angle from the positive a axis,
 	towards the positive b axis.