remove listings for old theming guides

src/app/routes.ts

@@ -19,6 +19,14 @@ export const MATERIAL_DOCS_ROUTES: Routes = [
   // Since https://github.com/angular/components/pull/9574, the cdk-table guide became the overview
   // document for the cdk table. To avoid any dead / broken links, we redirect to the new location.
   {path: 'guide/cdk-table', redirectTo: '/cdk/table/overview'},
+  // In v19, the theming system became based on system variables and the mat.theme mixin.
+  // The following guides were consolidated into the main theming guide, which redirects
+  // users to v18 docs if they are looking for this content.
+  {path: 'guide/theming-your-components', redirectTo: '/guide/theming'},
+  {path: 'guide/typography', redirectTo: '/guide/theming'},
+  {path: 'guide/customizing-component-styles', redirectTo: '/guide/theming'},
+  {path: 'guide/elevation', redirectTo: '/guide/theming'},
+  {path: 'guide/duplicate-theming-styles', redirectTo: '/guide/theming'},
   {
     path: 'guide/:id',
     loadChildren: () => import('./pages/guide-viewer').then(m => m.GuideViewerModule)

src/app/shared/guide-items/guide-items.ts

@@ -34,36 +34,12 @@ const GUIDES: GuideItem[] = [
     document: SystemVariables,
     overview: 'Understand the system variables available to use in your application.'
   },
-  {
-    id: 'theming-your-components',
-    name: 'Theming your own components',
-    document: '/docs-content/guides/theming-your-components.html',
-    overview: 'Use Angular Material\'s theming system in your own custom components.'
-  },
-  {
-    id: 'typography',
-    name: 'Customizing Typography',
-    document: '/docs-content/guides/typography.html',
-    overview: 'Configure the typography settings for Angular Material components.'
-  },
-  {
-    id: 'customizing-component-styles',
-    name: 'Customizing component styles',
-    document: '/docs-content/guides/customizing-component-styles.html',
-    overview: 'Understand how to approach style customization with Angular Material components.'
-  },
   {
     id: 'creating-a-custom-form-field-control',
     name: 'Custom form field control',
     document: '/docs-content/guides/creating-a-custom-form-field-control.html',
     overview: 'Build a custom control that integrates with `<mat-form-field>`.'
   },
-  {
-    id: 'elevation',
-    name: 'Elevation helpers',
-    document: '/docs-content/guides/elevation.html',
-    overview: 'Enhance your components with elevation and depth.'
-  },
   {
     id: 'creating-a-custom-stepper-using-the-cdk-stepper',
     name: 'Custom stepper using the CdkStepper',
@@ -76,12 +52,6 @@ const GUIDES: GuideItem[] = [
     document: '/docs-content/guides/using-component-harnesses.html',
     overview: 'Write tests with component harnesses for convenience and meaningful results.'
   },
-  {
-    id: 'duplicate-theming-styles',
-    name: 'Duplicate theming styles',
-    document: '/docs-content/guides/duplicate-theming-styles.html',
-    overview: 'Learn about our new color mixins for Sass that avoid duplicating theming styles.'
-  },
   {
     id: 'material-2-theming',
     name: 'Theming Angular Material with Material 2',