Which component of the web browser converts HTML and CSS into viewable content?

The component of the web browser that converts HTML and CSS into viewable content is the rendering engine. This engine interprets the HTML and CSS code and then displays the information in a way that is visually understandable to the user. It processes the elements of the web page, such as text, images, styles, and layouts, to present a complete and formatted interface that users interact with.

While the document viewer may serve to display the rendered output to the user, it does not play a role in the conversion process itself; that is the primary function of the rendering engine. Similarly, the user interface is concerned with how the user interacts with the browser, and the web server is responsible for serving web content rather than converting it for display. Thus, the rendering engine is central to transforming the structured data of a webpage into the visual format that users expect.