CSS is a document type that defines how an HTML document or web page should look like. A browser processes the content of CSS files before being rendered by the browser's rendering engine to create the webpage's layout and design. JS can be embedded in HTML5, CSS3, and other languages as a client-side scripting language. Although JavaScript and CSS are similar, they are not the same. They have different syntaxes and rules for how they work with each other. For example, JS requires curly braces, while CSS requires semicolons. JavaScript variables need to start with an uppercase letter, while CSS variables need to start with a lowercase letter, and so on.