[css-content] fix typo in example

Author: dauwhe

css-content/Overview.bs

@@ -349,7 +349,7 @@ Alternative text for Generated Content: The 'alt' property</h3>
   <pre>
   .new::before { 
     content: url(./img/star.png);
-    alt: "New!"; /* or a lcoalized attribute from the DOM: attr("data-alt") */
+    alt: "New!"; /* or a localized attribute from the DOM: attr("data-alt") */
   }
   </pre>
   </div>

css-content/Overview.html

@@ -417,7 +417,7 @@ <h3 class="heading settled" data-level=2.1 id=alt-property><span class=secno>2.1
 
   <pre>.new::before { 
   content: url(./img/star.png);
-  alt: "New!"; /* or a lcoalized attribute from the DOM: attr("data-alt") */
+  alt: "New!"; /* or a localized attribute from the DOM: attr("data-alt") */
 }
 </pre>
   </div>