If you haven’t already, you’ll soon discover that block themes sometimes leave you needing to make CSS adjustments.
A classic example is the title of this very website. You’ll see that the text is white, but it has a black shadow. How was that added?
If you enter your domain name followed by /wp-admin/customize.php, in the address bar of your browser, that will take you to the classic “Additional CSS” area where you can do everything you’ve always done with WordPress CSS.