[css-grid-1] Fix some typos. #3410

Author: fantasai

css-grid-1/Overview.bs

@@ -486,7 +486,7 @@ Placing Items</h3>
 			grid-area: auto;       /* Auto-place into next empty area    */
 			grid-area: 2 / 4;      /* Place into row 2, column 4         */
 			grid-area: 1 / 3 / -1; /* Place into column 3, span all rows */
-			grid-area: header-start / sidebar-start / footer-end / sidebar-start;
+			grid-area: header-start / sidebar-start / footer-end / sidebar-end;
 			                       /* Place using named lines            */
 		</pre>
 
@@ -497,7 +497,7 @@ Placing Items</h3>
 			grid-row: auto;                      grid-column: auto;
 			grid-row: 2;                         grid-column: 4;
 			grid-row: 1 / -1;                    grid-column: 3;
-			grid-row: header-start / footer-end; grid-column: sidebar-start / footer-end;
+			grid-row: header-start / footer-end; grid-column: sidebar-start / sidebar-end;
 		</pre>
 
 		They can further be decomposed into the 'grid-row-start'/'grid-row-end'/'grid-column-start'/'grid-column-end' longhands, e.g.