[css-overflow-3] Fix typo w3c#5468

Author: fantasai

css-overflow-3/Overview.bs

@@ -1156,7 +1156,7 @@ Forcing a Break After a Set Number of Lines: the 'max-lines' property</h3>
 				a: line 4<br>
 			</div>
 		</xmp>
-		Sample rendering given <code highlight=css>#a { line-clamp: 5; } b { line-clamp: 2; }</code>:
+		Sample rendering given <code highlight=css>#a { line-clamp: 5; } #b { line-clamp: 2; }</code>:
 		<pre>
 			a: line 1
 			a: line 2
@@ -1165,7 +1165,7 @@ Forcing a Break After a Set Number of Lines: the 'max-lines' property</h3>
 			a: line 3…
 		</pre>
 
-		Sample rendering given <code highlight=css>#a { line-clamp: 3; } b { line-clamp: 2; }</code>:
+		Sample rendering given <code highlight=css>#a { line-clamp: 3; } #b { line-clamp: 2; }</code>:
 		<pre>
 			a: line 1
 			a: line 2