cdnjs is a free distributed JS library delivery service.
Font Awesome is a font and icon toolkit based on CSS and Less.
HTTP Strict Transport Security (HSTS) informs browsers that the site should only be accessed using HTTPS.
Materialize CSS is a front-end framework that helps developers create responsive and mobile-first web applications. It is based on Google's Material Design guidelines.
PHP is a general-purpose scripting language used for web development.