Ooh, good catch! Looks like I missed adding that to the style. I've fixed it on GitHub, and I'll upload it again here shortly; in the meantime, you can see the fix here on lines 67-68: https://github.com/shawna-p/EasyRenPyGui/blob/main/game/screens/dialogue_screens...
If you're ever having trouble finding a style property (like the size of the font), don't forget you can hover over it and hit shift+i to get the Displayable Inspector! If you do so hovering over the name, it'll tell you that the size comes from style say_label, which you can then search the project for and find in the dialogue_screens.rpy file (which is where the fix went!).