Hi,
Unless you’re adding thousands of lines of CSS codes, using the default blog page should be better for speed.
Do I then add the CSS to Customize>Additional CSS?
If you specifically want to target the blog post entries then yes, you’ll have to add custom CSS. ๐
But since you only need to add padding, the code should be as short as .your-selector-here{padding:30px}
and that’s basically it as opposed to adding a plugin.
Although, WP Show Posts should be pretty fast to as it is also lightweight itself. ๐