Font size for running text

Dear Kathryn,
sorry for the next question ?? Is it possible to increase the font size for the running text? There are so many different css classes and everything I tried didn′t work ;( I just tried to expand the p style in line 151 of the style.css:

p {
  margin-bottom: 24px;
}

to

p {
  margin-bottom: 24px;
font-size: 18px;
}

But if I do it this way the blockquotes are also 18px ;(

Sorry for the next noob question, but I am more a graphic than a css person ??