Let's take the newsletter subscription template as an example.
Change the pop-in's background
Change the size of the pop-in
Change the size of your text font through CSS
Add your own font to the element
To add your font to your pop-in you import it in the custom CSS block.
Here is an example:
The code is:
@font-face {
font-family: "Name of your font";
src: url(https://www.poool/fonts/poool.woff2);
}