Shading words or paragraphs gives them a background color that updates when you switch to a different document theme. It's different from highlighting text, which has a very limited choice of colors, and doesn't update when you switch to another theme.
Select the word or paragraph that you want to apply shading to.
On the Home tab, in the Paragraph group, click the arrow next to Shading.
Under Theme Colors, click the color that you want to use to shade your selection.
Note: If you want to use a color that isn't a theme color, choose one under Standard Colors or click More Colors. If you switch to a different theme, only theme colors will update.
For information about using shading in tables, see Add or remove shading in a table.
For information about using document theme colors, see Apply, customize, and save a document theme in Word or Excel.