Enlarge text size in "about us" and "services" sections

Hallo!
How can I enlarge the text size in the “about us” and “services” sections? I downloaded the earlier recommended CSS-Plugin and would appreciate if I could get the corresponding piece of code to alter the text size for the two sections. The text is very small and customers keep complaining, they can’t read it… https://www.annawaetjen.de
Thank you!