Go to the Tax display page > Click on the Tax display setting you have created:
Scroll down to the bottom of the page and check on your right-handed bar, there is a Design section:
Display price type: Manage how the pricing should be displayed, you can either show only price with/without tax or both prices:
Ratio between Excl tax & Incl tax font size: Set the font size ratio between the two prices (only applies if you’ve selected “Both prices” in the Display Price Type setting).
By default, the app uses a 1:1 ratio, meaning both prices will appear with the same font size. You can change to other ratios available in the dropdown list.