[css-inline-3] Better link to HTML

Author: fantasai

css-inline-3/Overview.bs

@@ -2673,7 +2673,7 @@ A.1: Calculating [=Em-over=] and [=Em-under=]</h3>
 	Note: The [=em-over=] and [=em-under=] baselines are not used by CSS.
 	Their definitions are included in this module
 	for consistency with the other metrics used by
-	<a href="https://html.spec.whatwg.org/multipage/canvas.html#2dcontext">Canvas 2D API</a>.
+	<a href="https://html.spec.whatwg.org/multipage/canvas.html#textmetrics">Canvas TextMetrics API</a>.
 
 	The [=em-over=] and [=em-under=] metrics are calculated as follows: