A developer designs and implements the visual layout and aesthetics of websites and web applications. They use , the latest version of the Cascading Style Sheets language, to control colors, fonts, spacing, animations, and transitions, ensuring optimal user experience across various devices and browsers. They also work collaboratively with other developers to integrate the CSS with HTML and JavaScript code. Additionally, they follow the best practices for responsive design, performance optimization, and accessibility standards. They are also responsible for debugging, maintaining, and enhancing the CSS code as needed to keep the user interface modern and functional.