How does a browser work?

The browser processes the user request, retrieves resources from the server (HTML, CSS, JS), parses HTML, builds the DOM tree, parses CSS, builds the CSSOM tree. Then it combines the DOM and CSSOM into the Render Tree, which contains only visible elements. It performs Layout, determining the position and size of elements. Finally, Paint occurs, rendering pixels on the screen. JavaScript is executed, which can modify the DOM and CSSOM, triggering re-rendering. The browser optimizes the process using caching, lazy loading, and asynchronous operations.