Which of the following describes a common functionality of multiple HTML files?

Multiple HTML files often share a single CSS file for styling, which is a fundamental aspect of web development. This approach allows for a consistent look and feel across multiple web pages without the need to duplicate the same CSS code in each HTML file. By linking to a common stylesheet, developers can maintain ease of updates and modifications; any changes made to the CSS file will reflect across all HTML files that utilize it. This practice not only promotes efficiency in coding but also ensures that the site remains cohesive in design and user experience.

The other options present misconceptions about the relationship between HTML files. While it is true that HTML files can be used independently, they are typically more effective when they are interconnected. Being located in the same directory is helpful but not a requirement for HTML files to function collectively. Lastly, interaction with JavaScript is very much possible; HTML files can include JavaScript files to enhance functionality and user interactivity, making that option incorrect as well.