Clarified constraints for text-decoration-thickness length and percentage

The current sentence could be interpreted as performing a `floor` on the actual calculated value, while it is actually rounded to the nearest integer, with a minimum value of one.
Equivalent to: `x = min(1, round(x))`

Author: tcaptan-cr

css-text-decor-4/Overview.bs

@@ -339,15 +339,17 @@ Text Decoration Line Thickness: the 'text-decoration-thickness' property</h3>
 		<dt><dfn><<length>></dfn>
 		<dd>
 			Specifies the thickness of text decoration lines as a fixed length.
-			The UA must floor the actual value at one device pixel.
+			The UA should round the actual value to the nearest integer,
+			and ensure it is at least one device pixel.
 
 			Note: A length will inherit as a fixed value,
 			and will not scale with the font.
 
 		<dt><dfn><<percentage>></dfn>
 		<dd>
 			<p>Specifies the thickness of text decoration lines as a percentage of ''1em''.
-			The UA must floor the actual value at one device pixel.
+			The UA should round the actual value to the nearest integer,
+			and ensure it is at least one device pixel.
 
 			Note: A percentage will inherit as a relative value,
 			and will therefore scale with changes in the font as it inherits.