[css-inline-3] Fix heading, issue.

Author: fantasai

css-inline-3/Overview.bs

@@ -294,8 +294,8 @@ Baseline Metrics</h3>
 	they must be synthesized,
 	see [[#baseline-tables]] and [[#baseline-synthesis]].
 
-<h4 id="baseline-tables">
-Baselines of Glyphs and Boxes</h4>
+<h3 id="baseline-tables">
+Baselines of Glyphs and Boxes</h3>
 
 	Each font, glyph, and [=inline-level box=]
 	is assumed to have a [=baseline=] coordinate
@@ -348,7 +348,7 @@ Line Heights and Content Alignment</h2>
 				For [=inline boxes=] with ''line-sizing: normal'',
 				this is their [=outer size=].
 
-				Issue: Handle negative half-leading?
+				Issue(5178): Handle negative half-leading?
 		</ul>
 
 	2. The [=inline-level boxes=] are aligned in the [=block axis=]