Every website you visit runs on a combination of three technologies. While modern web frameworks simplify development, they still compile down to HTML, CSS, and JavaScript.
Understanding how these three layers interact is fundamental to building websites that load quickly and work reliably on all devices.
HTML: the structural blueprint
HyperText Markup Language (HTML) is the skeleton of any web page. It defines the raw content and semantic structure of a document using tags.
Without HTML, web browsers would not know where a paragraph ends, where an image should appear, or what text is a button. When you write standard HTML, you are declaring what elements belong on the page.
To practice writing semantic markup, experiment with elements inside our HTML playground.
CSS: the styling layer
Cascading Style Sheets (CSS) determines how those HTML elements look. It controls layouts, typography, colors, and responsive designs that adapt to screen sizes.
Modern CSS supports variables, grid layouts, and hardware-accelerated animations. Separating style from structure allows you to completely change a website’s appearance without touching the underlying HTML.
You can test styles, gradients, and layouts live using our dedicated CSS playground.
JavaScript: the interactive engine
JavaScript brings your pages to life. It is a scripting language that runs inside the user’s browser, allowing you to update content dynamically without reloading the page.
When a user clicks a button, submits a form, or toggles dark mode, JavaScript handles that event. It can also fetch new data from servers in the background and update the HTML on the fly.
To write and test interactive scripts, open our JavaScript playground to see console logs in real time.
Collaborating in the browser
When a browser loads a web page, it parses the HTML first to build the Document Object Model (DOM). It then parses the CSS to apply styles, and finally executes JavaScript to register event handlers. Writing clean code in all three layers ensures a fast, accessible experience for your users.
For quick references, see our HTML Tags Cheatsheet and CSS Flexbox Cheatsheet.