Angular 7 dynamic themes made simple with native css variables

Example of usage: view on stackblitz

Usage:

npm i ngx-themes --save

app.module.ts

import  {  BrowserModule  }  from  '@angular/platform-browser';
import  {  NgModule  }  from  '@angular/core';
import  {  AppComponent  }  from  './app.component';

import  {  NgxThemesModule  }  from  'ngx-themes';
import  {  LightTheme  }  from  './themes/light';
import  {  DarkTheme  }  from  './themes/dark';

@NgModule({
declarations:  [
    AppComponent
],
imports:  [
    BrowserModule,
    NgxThemesModule.forRoot({
	    themes:  [LightTheme,  DarkTheme],
	    active:  'lightTheme'
    }),
],
providers:  [],
bootstrap:  [AppComponent]
})
export  class  AppModule { }

./themes/dark.ts

export  const  DarkTheme  =  {
    name:  'darkTheme',
    properties:  {
	    '--primary-color':  '#3e3e3e',
	    '--on-primary-color':  '#fff',
    }
};

.themes/light.ts

export  const  LightTheme  =  {
    name:  'lightTheme',
    properties:  {
	    '--primary-color':  '#d9d9d9',
	    '--on-primary-color':  '#919191',
    }
};

Apply themes in components

In order to use the themes in templates, apply "ngx-theme" directive on you html tags. e.g. :

<button  ngx-theme> </button>

In your css/less/scss file, style the button using css variables defined in your themes. e.g.:

button {
    background: var(--primary-color);
    color: var(--on-primary-color);
    border: none;
    width: 300px;
    height: 40px;
    outline: none;
    cursor: pointer;
}

Change themes at runtime

In order to change the themes, you need to use the "ThemeService" provided by ngx-themes. e.g.: app.component.ts

import  {  Component  }  from  '@angular/core';
import  {  ThemeService  }  from  'ngx-themes';

@Component({
    selector:  'app-root',
    templateUrl:  './app.component.html',
    styleUrls:  ['./app.component.less']
})
export  class  AppComponent {
    currentTheme =  '';
    constructor(private themeService:  ThemeService) {
	    this.currentTheme  =  themeService.getActiveTheme().name;
    }

    toggleTheme() {
	    if (this.currentTheme  ===  'lightTheme') {
		    this.themeService.setTheme('darkTheme');
		    this.currentTheme  =  'darkTheme';
	    } else {
		    this.themeService.setTheme('lightTheme');
		    this.currentTheme  =  'lightTheme';
	    }
    }
}