You could try something like this - but there are a few spots where it probably won't apply the new font size and you'll have to add more rules. This assumes you want all the fonts to be larger:
:root{
font-size:larger !Important;
}
You'll most likely have to modify the font in a few places here are some examples of increasing the font size for the item cards and the bottom panel title
:root{
--calcite-font-size--2: 1.5rem;
}
.esri-portfolio__body--carousel .esri-portfolio-carousel{
font-size:1.4em;
}