eXtensible Application Markup Language
XAML, short for Extensible Application Markup Language, is a declarative XML-based language used to define user interfaces and layout in applications, particularly within the .NET ecosystem. Developed by Microsoft, XAML enables developers to separate UI design from business logic, facilitating a clear Model-View-ViewModel (MVVM) architecture.
CSS
CSS, short for Cascading Style Sheets, is a style sheet language used to describe the presentation of HTML and XML documents, including web pages, user interfaces, and mobile applications. Developed by Håkon Wium Lie and Bert Bos in 1996, CSS can be downloaded and used directly in any modern web browser or incorporated into projects via frameworks like Bootstrap.