The first two are controlled by the CSS coding on your site. You have to edit or create custom CSS to overwrite that and get the correct spacing and remove the line.

As for the word “optional,” you can’t easily remove that. You’d have to edit the plugin’s PHP code or find a way to hook into it from your child theme’s function.php file.

Thanks @DavidSandel - very helpful!

Just one more question: is it possible to check the box by default? I remember Mailchimp had this option, but can’t find it in Klaviyo.

It’s not available in the settings, but you can force that to happen using CSS as well.