Should you want to change your widget's text font size, kindly follow the steps below:
1. From your dashboard, go to the On-Site Widgets
2. On the Customization page, scroll down to the Formatting settings area.
3. Under the Font Size category, choose the font sizes you want for review titles and review texts. Click on the dropdown to pick a size.
4. Save your changes. Your widget text font size should be changed.