[css-conditional-5] Evaluating unitless zero against <length> values … (#12656)

* [css-conditional-5] Evaluating unitless zero against <length> values in style ranges

* Applied review comments

Author: tursunova

css-conditional-5/Overview.bs

@@ -1371,7 +1371,8 @@ Style Container Features</h3>
 			<<number>>, <<percentage>>, <<length>>, <<angle>>, <<time>>, <<frequency>> or <<resolution>>.
 			If this cannot be done, evaluate to false.
 		4. If each <<style-range-value>> from the range have the same type,
-			compute each and evaluate the comparison.
+			compute each and evaluate the comparison;
+			a unitless zero must be treated as being a zero-<<length>> when compared against a <<length>> .
 		5. Otherwise evaluate to false.
 	</div>