- After your text is on the screen, click Shapes to the left of the screen (under the More section) and select the rectangle shape
- Click on the Fill color option - change to the highlight color you want
- Click on the Outline color option - change to the highlight color
- Click on the rectangle shape again to place it on your text box
- Click on the shape image in the middle of the screen to select it and at the top of the screen click Arrange
- Select Send to Back, which will move the color behind the text
- You can drag the size of the shape to cover all of your text

Shapes work slightly differently in the downloaded software:
Click on Basic and choose rectangle shape and the shape will appear on your screen
To the left of the screen you can choose your highlight color

Click on the color to the right of Line and Fill to choose your highlight color