Cookies, Response Codes, and Headers
There is more to HTTP than just sending HTML, CSS, and JS. Cookies are small pieces of data that are stored on your computer. They are used to store information about you, such as your session and other preferences. Cookies are sent to the server with every request, and the server can use this information to customize your experience. Response codes are numbers that are sent back to the browser to indicate the status of the request. The most common response codes are 200, which means the request was successful, and 404, which means the content was not found. Headers are pieces of information that are sent with every request. They contain information about the request, such as the browser and OS (also known as a " user agent"), the IP address of the client, and other information used to identify the request.
Client-Side vs Server-Side
Remember, client-side code is visible to you. Most browsers support viewing the page source. It's known as "Inspect", "Inspect Element", or "View Page Source". Try to take a look around at the source of this page and see if you can find any flags. Make sure to analyze all three: HTML, CSS, and JS.