How Browsers Convert HTML, CSS, and JavaScript Into Pixels on Screen

When a browser loads a webpage, it processes HTML, CSS, and JavaScript through a multi-step rendering pipeline before displaying anything on screen. First, the browser parses HTML into a tree-like structure called the DOM, then converts CSS rules into a parallel structure called the CSSOM. These two structures are merged into a Render Tree, which includes only the elements that are actually visible on the page. The browser then runs a Layout phase to calculate the exact size and position of every element, followed by a Paint phase that draws visual details like colors, borders, and text. Finally, the painted layers are composited together to produce the finished pixels that appear on the user's screen.