Update index.md

Author: BAndysc

docs/basics/user-interface/styling/themes/index.md

@@ -27,4 +27,8 @@ Several themes, in varying stages of development, have been brought to life by o
 
 ### Semi.Avalonia
 
-- [Semi.Avalonia](https://github.com/irihitech/Semi.Avalonia) is inspired by [Semi Design](https://semi.design/en-US)
+- [Semi.Avalonia](https://github.com/irihitech/Semi.Avalonia) is inspired by [Semi Design](https://semi.design/en-US)
+  
+### Classic.Avalonia
+
+- [Classic.Avalonia](https://github.com/BAndysc/Classic.Avalonia) is a classic theme inspired by the design of Windows 9x family.