Hi there, you have a flexible tool in custom css

for example to change the overall properties of paragraph's font:

p {
    font-size: 18px;
    line-height: 28px;
   .. add here more properties
}

or depending of context

for example

.maestro_portfolio-template-default p {
    font-size: 18px;
}

will change the font size only in single portfolio pages.

Add the code in theme options -> styling options -> custom CSS or customizer