[css-values-4] Fix typo

Author: fantasai

css-values-4/Overview.bs

@@ -934,7 +934,7 @@ Relative lengths</h3>
 Font-relative lengths: the ''em'', ''ex'', ''cap'', ''ch'', ''ic'', ''rem'', ''lh'', ''rlh'' units</h4>
 
 	The <dfn export id="font-relative-length">font-relative lengths</dfn> refer to the font metrics of the element on which they are used,
-	or, in the case of ''rem'' and ''rlh'', the metrics of the root element).
+	or, in the case of ''rem'' and ''rlh'', the metrics of the root element.
 
 	<figure>
 		<img src="images/Typography_Line_Terms.svg" alt="The word 'Sphinx' annotated with various font metrics: ascender height, to the top of the h's serif; cap height, to the visually approximate top of the S; the x height, to the visually approximate top of the x; the baseline, along the bottom of S, h, i, n, and x; and the descender height, to the bottom fo the p.">