First select your cells and go under Home tab into Styles section. Choose the first button from the row called “Conditional Formatting”. From there choose “Top/Bottom Rules” and “Top 10 Items …” In the menu you can choose the number of top values shown. By default the number is 10. From the right sided drop-down menu select the style you wish to apply. Notice that some only apply to text or background whilst others format both of those. If you are satisfied, click on “OK”.