Bootstrap is a free and open-source CSS framework directed at responsive, mobile-first front-end web development. It contains CSS and JavaScript-based design templates for typography, forms, buttons, navigation, and other interface components.
Buy me a coffee is a service for online content creators that they may use to receive tips and donations to support their work.
cdnjs is a free distributed JS library delivery service.
HTTP Strict Transport Security (HSTS) informs browsers that the site should only be accessed using HTTPS.