[css-align] Add an lt for 'synthesized baseline'.

Author: tabatkins

css-align/Overview.bs

@@ -1827,7 +1827,7 @@ Determining the Baselines of a Box</h2>
 	use the baseline table from the font settings and <a>first available font</a> of that box,
 	and align that baseline set to the given single baseline.
 
-	To <dfn local-lt=synthesize|synthesized export>synthesize baselines</dfn> from a rectangle (or two parallel lines),
+	To <dfn lt="synthesize baseline|synthesized baseline" local-lt=synthesize|synthesized export>synthesize baselines</dfn> from a rectangle (or two parallel lines),
 	synthesize the alphabetic baseline from the <a>line-under</a> line,
 	and the central baseline by averaging the positions of the two edges or lines.
 	See [[css-inline-3#baseline-synthesis]] for rules on synthesizing additional baselines.