A static website as the name suggest is a site where the content remains the same unless until it is manually updated by the developer or website administrator. Static websites offer significant advantages in terms of performance, security, simplicity, and cost-effectiveness. They are particularly well-suited for projects with fixed content, high traffic expectations, and a need for fast load times and reliability.
CSS
While working with Drupal (10), you would want to inject/add some of your own CSS/JavaScript without modifying the actual theme CSS.