[css-round-display] Fix percentages line of polar-angle propdef (ACTION-707: https://www.w3.org/Style/CSS/Tracker/actions/707)

Author: hyojinLGE

css-round-display/Overview.bs

@@ -297,7 +297,7 @@ The 'polar-angle' property specifies the angle from the X-axis (or a fixed direc
     Initial: 0
     Media: visual
     Inherited: no
-    Percentages: relative to radius of circle
+    Percentages: n/a
 	Animatable: as <angle>
 </pre>
 <h3 id="polar-distance-property">The 'polar-distance' property</h3>