To preview a theme in your document, hold your mouse over a theme in this drop-down menu. Then click the “Themes” drop-down button in the “Document Formatting” button group to show a drop-down menu of theme choices. To apply a theme in Word to a document, click the “Design” tab in the Ribbon. A theme in Word is a collection of a style set, color set, font set, effects, and paragraph spacing you can apply to your document. You can easily apply a theme in Word to your document.