HTML presents the content of a webpage, while CSS defines its visual appearance. Programming languages, on the other hand, determine the functionality of a webpage. HTML can provide simple links and basic interactivity, but for highly interactive features like checkouts, commenting, and social media posting, programming languages are essential. While there are many programming languages, JavaScript is the most commonly used on the web today. At their core, all programming languages use “if/then” statements. For example, “if the user clicks a certain button, then display a popup dialog.” This book focuses solely on HTML and CSS, but it’s crucial to have a basic understanding of programming languages and their role in web interaction.