To highlight multiple items on a web page, you need to select all the elements you want to change and then modify their appearance. Suppose you have a list of items and you want to highlight them by changing their background color. You can do this by first selecting all the list items using a method like querySelectorAll, which returns a collection of elements. Once you have this collection, you can loop through each item and update its style. This approach is useful when you want to apply the same change to several elements at once, such as highlighting all tasks in a to-do list or marking important entries in a table.