text: Style sets and themes let you completely change the look of your document in an instant. They 
  work best when your document is formatted with styles (so it’s good that we fixed that Heading 
  style, above). 
  
  Try it: Explore style sets and themes: 
  
  1. On the Design tab, select Themes, and choose a theme from the drop-down. 
  Notice that the gallery of style sets updates to reflect the theme you picked. 
  
  2. Select any theme you like from the drop-down and click to apply. 