Hello, Tell me how CSS used in SEO
In the sense that CSS is used to style and present the content which you create, which aids your users' experience, is recognised by various Google/Bing algorithms and helps your page SERP?
CSS indirectly affects SEO, but isn't really related.
Cascading Style Sheets, a new feature being added to HTML that gives both Website developers developers and users more control over how pages are displayed. With CSS, designers and users can create style sheets that define how different elements, such as headers and links, appear. These style sheets can then be applied to any Web page.