$( "li.third-item" ).prev().css( "background-color", "red" );
Here is what the above code is Doing:
1. Select the first list item within the first unordered list.
2. Select the last list item within the first unordered list.
3. Select all list items that are siblings of the first list item.
4. Select the next sibling of each list item.
5. Select the previous sibling of each list item.