The job duties of an HTML/CSS developer involve working to create, update, test, or refine websites and applications. Your responsibilities in this career focus on front-end web and application development. You program and develop sites using HTML and CSS languages. You often work within an existing framework and add or edit the code to create a website or system that fits the needs of your client or employer. You also use computer software to add visual elements and test your code. An HTML/CSS developer sometimes configures webmaster-facing applications for advertisement or data collection purposes.