[css-multicol-1][editorial] Gloss "in-flow"/"out-of-flow" jargon (#13072)

Backport of #13071

Author: cvrebert

css-multicol-1/Overview.bs

@@ -356,7 +356,7 @@ The Multi-Column Model</h2>
 		</figure>
 	</div>
 
-	Out-of-flow descendants of a [=multi-column container=] do affect column balancing,
+	[=Out-of-flow=] descendants of a [=multi-column container=] do affect column balancing,
 	and the block-size of the [=multi-column container=].
 
 	<wpt>
@@ -1293,7 +1293,7 @@ Spanning Columns</h2>
 	Name: column-span
 	Value: none | all
 	Initial: none
-	Applies to: in-flow block-level elements
+	Applies to: [=in-flow=] block-level elements
 	Inherited: no
 	Percentages: N/A
 	Computed value: specified keyword