[css-align-3] Add images.

Author: fantasai

css-align-3/Overview.bs

@@ -1105,6 +1105,10 @@ Overflow and Scroll Positions</h3>
 	on <em>both</em> sides of the <a>scrollable overflow region</a>.
 	See [[css-overflow-3]] for details.)
 
+	<figure>
+		<img src="images/scroll-align-padding.jpg" alt="">
+	</figure>
+
 	ISSUE: Coordinate wording with css-overflow once it's less of a mess.
 
 	None of this changes how scroll coordinates are assigned:
@@ -1118,6 +1122,12 @@ Overflow and Scroll Positions</h3>
 	grows the <a>scrollable overflow region</a> but not the <a>alignment subject</a>,
 	thus an ''align-content/end''-aligned <a>scroll container</a>
 	might not be initially scrolled all the way to the bottom.
+	<figure>
+		<img src="images/scroll-align-overflow.jpg" alt="">
+		<figcaption>Overflow is not part of the <a>alignment subject</a>,
+		even for a <a>scroll container</a>.</figcaption>
+	</figure>
+
 
 <h3 id="baseline-align-content">
 Baseline Content-Alignment</h3>