docs(angular): consolidate duplicate theming topics into themes/index.mdx

docs/angular/src/content/en/components/general/cli/step-by-step-guide-using-angular-schematics.mdx

@@ -79,7 +79,7 @@ If you select **side-nav** or **side-nav-mini**, the wizard will prompt you with
 Two theme options are available:
 
 - **default** - includes a pre-compiled CSS file (`igniteui-angular.css`) with the default Ignite UI for Angular Material-based theme in `angular.json`
-- **custom** - generates a color palette and theme configuration using the [Theming API](../../themes.mdx) in `app/styles.scss`, ready for customization
+- **custom** - generates a color palette and theme configuration using the [Theming API](../../themes/sass/index.mdx) in `app/styles.scss`, ready for customization
 
 <Image src={igStepByStepNewProjectTheme} alt="Step by step prompt: choose default or custom theme" class="responsive-img" />
 

docs/angular/src/content/en/components/general/cli/step-by-step-guide-using-cli.mdx

@@ -67,7 +67,7 @@ If you select **Side Navigation** or **Side Navigation Mini**, the wizard will p
 
 <Image src={igStepByStepNewProjectQuestion} alt="Step by step auth question prompt" class="responsive-img" />
 
-The next step is to choose a theme for your application. Selecting the default option includes a pre-compiled CSS file (`igniteui-angular.css`) with the default Ignite UI for Angular theme in your project's `angular.json`. The custom option generates a color palette and theme configuration using the [Theming API](../../themes.mdx) in `app/styles.scss`.
+The next step is to choose a theme for your application. Selecting the default option includes a pre-compiled CSS file (`igniteui-angular.css`) with the default Ignite UI for Angular theme in your project's `angular.json`. The custom option generates a color palette and theme configuration using the [Theming API](../../themes/sass/index.mdx) in `app/styles.scss`.
 
 <Image src={igStepByStepNewProjectTheme} alt="Step by step new project theme selection" class="responsive-img" />
 

docs/angular/src/content/en/components/general/getting-started.mdx

@@ -88,7 +88,7 @@ If you already have an Angular project or prefer to work entirely within the Ang
 ng new <project-name> --style=scss
 ```
 
-SCSS is recommended because the [Ignite UI for Angular Theming Library](../themes.mdx) is built on it and `ng add` configures the default theme automatically. Then add Ignite UI for Angular:
+SCSS is recommended because the [Ignite UI for Angular Theming Library](../themes/sass/index.mdx) is built on it and `ng add` configures the default theme automatically. Then add Ignite UI for Angular:
 
 ```cmd
 ng add igniteui-angular