Is there also a way to make the font bigger in the widgets sidebar on the right side of the post pages?
To adjust the font size for widgets in the right sidebar for posts in the Suburbia theme, start with this and adjust the size to your liking:
.widget h3.widget-title {
font-size: 150%;
}
.widget {
font-size: 130%;
}
Note that it's possible that some widgets or widget areas will have a font size set with an additional selector that it more specific. If you find that happening for any sidebar text, then you just need to identify that selector and add a rule to override it in your CSS.
It's also possible to set the font for certain types of widgets or specific widgets individually. If you want to do that, you need to look at the page source in your browser to see what classes or IDs are set in the HTML and use those to create more specific CSS. For example, You can change just the categories widget fonts like this:
.widget_categories h3.widget-title {
font-size: 150%;
}
.widget_categories {
font-size: 130%;
}