egghead: Use :host-context and the ::ng-deep selector to apply context-based styling

<!DOCTYPE html>
<html>

  <head>
    <base href="." />
    <title>angular playground</title>
    <link rel="stylesheet" href="style.css" />
    <script src="https://unpkg.com/core-js@2.4.1/client/shim.min.js"></script>
    <script src="https://unpkg.com/zone.js/dist/zone.js"></script>
    <script src="https://unpkg.com/zone.js/dist/long-stack-trace-zone.js"></script>
    <script src="https://unpkg.com/reflect-metadata@0.1.3/Reflect.js"></script>
    <script src="https://unpkg.com/systemjs@0.19.31/dist/system.js"></script>
    <script src="config.js"></script>
    <script>
    System.import('app')
      .catch(console.error.bind(console));
  </script>
  </head>

  <body>
    <my-app>
    loading...
  </my-app>
  </body>

</html>

/* Styles go here */

### Angular Starter Plunker - Typescript

System.config({
  //use typescript for compilation
  transpiler: 'typescript',
  //typescript compiler options
  typescriptOptions: {
    emitDecoratorMetadata: true
  },
  paths: {
    'npm:': 'https://unpkg.com/'
  },
  //map tells the System loader where to look for things
  map: {
    
    'app': './src',
    
    '@angular/core': 'npm:@angular/core/bundles/core.umd.js',
    '@angular/common': 'npm:@angular/common/bundles/common.umd.js',
    '@angular/compiler': 'npm:@angular/compiler/bundles/compiler.umd.js',
    '@angular/platform-browser': 'npm:@angular/platform-browser/bundles/platform-browser.umd.js',
    '@angular/platform-browser-dynamic': 'npm:@angular/platform-browser-dynamic/bundles/platform-browser-dynamic.umd.js',
    '@angular/http': 'npm:@angular/http/bundles/http.umd.js',
    '@angular/router': 'npm:@angular/router/bundles/router.umd.js',
    '@angular/forms': 'npm:@angular/forms/bundles/forms.umd.js',
    '@angular/animations': 'npm:@angular/animations/bundles/animations.umd.js',
    '@angular/platform-browser/animations': 'npm:@angular/platform-browser/bundles/platform-browser-animations.umd.js',
    '@angular/animations/browser': 'npm:@angular/animations/bundles/animations-browser.umd.js',
    
    '@angular/core/testing': 'npm:@angular/core/bundles/core-testing.umd.js',
    '@angular/common/testing': 'npm:@angular/common/bundles/common-testing.umd.js',
    '@angular/compiler/testing': 'npm:@angular/compiler/bundles/compiler-testing.umd.js',
    '@angular/platform-browser/testing': 'npm:@angular/platform-browser/bundles/platform-browser-testing.umd.js',
    '@angular/platform-browser-dynamic/testing': 'npm:@angular/platform-browser-dynamic/bundles/platform-browser-dynamic-testing.umd.js',
    '@angular/http/testing': 'npm:@angular/http/bundles/http-testing.umd.js',
    '@angular/router/testing': 'npm:@angular/router/bundles/router-testing.umd.js',
    
    'rxjs': 'npm:rxjs',
    'typescript': 'npm:typescript@2.2.1/lib/typescript.js'
  },
  //packages defines our app package
  packages: {
    app: {
      main: './main.ts',
      defaultExtension: 'ts'
    },
    rxjs: {
      defaultExtension: 'js'
    }
  }
});

//main entry point
import {platformBrowserDynamic} from '@angular/platform-browser-dynamic';
import {AppModule} from './app';

platformBrowserDynamic().bootstrapModule(AppModule)

//our root app component
import {Component, NgModule } from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'
import { FormsModule } from '@angular/forms';

import { HostContextStylingComponent } from './host-context.component';
import { ChildComponent } from './child.component';

@Component({
  selector: 'my-app',
  template: `
    <div class="styled-component">
      <hostcontext-styling></hostcontext-styling>
    </div>
  `,
})
export class App { }

@NgModule({
  imports: [ BrowserModule, FormsModule ],
  declarations: [ App, HostContextStylingComponent, ChildComponent ],
  bootstrap: [ App ]
})
export class AppModule {}

import { Component } from '@angular/core';

@Component({
  selector: 'hostcontext-styling',
  template: `
    <div>
      I'm a div that wants to be styled
    </div>
    <child-component></child-component>
  `,
  styles: [
    `
      /* apply a border if any of our ancestors has .styled-component applied */
      :host-context(.styled-component) {
        border: 1px solid gray;
        display:block;
      }
      
      :host ::ng-deep p {
        background-color: yellow;
      }
    `
  ]
})
export class HostContextStylingComponent {
}

import { Component } from '@angular/core';

@Component({
  selector: 'child-component',
  template: `
    <p>I am the child</p>
  `
})
export class ChildComponent {}