Add basic-theme index page

docs/en/ui-themes/basic-theme/index.md

@@ -1 +1,17 @@
-Read this document [here](../../framework/ui/mvc-razor-pages/basic-theme.md).
+# Basic Theme
+
+The Basic Theme is a minimalist theme that doesn't add any styling on top of the plain [Bootstrap](https://getbootstrap.com/) styles. You can take the Basic Theme as the base theme and build your own theme or styling on top of it. Here, a screenshot from the theme:
+
+![basic-theme-application-layout](../../images/basic-theme-application-layout.png)
+
+
+See the [Theming document](../../framework/ui/mvc-razor-pages/theming.md) to learn about themes.
+
+## User Interfaces
+
+The Basic Theme has implementation for the following UI types:
+
+- [MVC UI](../../framework/ui/mvc-razor-pages/basic-theme.md)
+- [Blazor UI](../../framework/ui/blazor/basic-theme.md)
+- [Angular UI](../../framework/ui/angular/basic-theme.md)
+