[css-snappoints] Update figcaption for example 2

Author: ChumpChief

css-snappoints/Overview.bs

@@ -143,10 +143,7 @@ Ignored Terms: scroll-snap-positions-*, containing block chain
 
             <figcaption>
                 The layout of the scroll container's contents in the example.
-                The snap-destination is horizontally centered and offset 100px from the top edge with respect to the scroll container's visual viewport
-                (represented by a red X),
-                and each element has its snap coordinate horizontally centered and top-aligned with respect to the element
-                (represented by yellow plus signs).
+                The snap alignment container is represented by the red rectangle (inset from the top by 100px due to the scroll-snap-padding), and the snap area is represented by the yellow rectangle.  Since the scroll-snap-align is "start" in the Y axis, a snap position is established at each scroll offset which aligns the Y-start of the snap alignment container (represented by a red dotted line) with the Y-start of a snap area (represented by a yellow dotted line).
             </figcaption>
         </figure>
     </div>