A basic CSS developer designs and builds user interfaces for websites and web applications. They use Cascading Style Sheets (CSS), a styling language, to control the layout and appearance of webpages. This includes designing elements such as fonts, colors, spacing, and responsive layouts. They often work alongside HTML and JavaScript developers to implement their designs and ensure they work across different browsers and platforms. Additionally, they optimize web pages for performance and maintain the standard coding conventions. They may also participate in user testing, fix bugs, and make improvements based on user feedback.