[css-shapes-1] Specify pair of length+percentage as <length-percentage> w3c#402

Author: fantasai

css-shapes-1/Overview.bs

@@ -524,7 +524,7 @@ Computed Values of Basic Shapes</h3>
 			Omitted values are included and compute to their defaults.
 		</li>
 		<li>
-			A <<position>> value in ''circle()'' or ''ellipse()'' is computed as a pair of offsets (horizontal then vertical) from the top left origin, each given as a combination of an absolute length and a percentage.
+			A <<position>> value in ''circle()'' or ''ellipse()'' is computed as a pair of offsets (horizontal then vertical) from the top left origin, each given as a <<length-percentage>>.
 		</li>
 		<li>
 			A <<'border-radius'>> value in ''inset()'' is computed as an expanded list of all eight <<length-percentage>> values.