I think i understood your problem and here is a solution for you :)
So when you create a new ng-project with the cli with opt in material-theming, you will get a inital theming configuration like the following (or you can find the config in the Material Guides)
import '~@angular/material/theming';
// Plus imports for other components in your app.
// Include the common styles for Angular Material. We include this here so that you only
// have to load a single css file for Angular Material in your app.
// Be sure that you only ever include this mixin once!
@include mat-core();
// Define the palettes for your theme using the Material Design palettes available in palette.scss
// (imported above). For each palette, you can optionally specify a default, lighter, and darker
// hue. Available color palettes: https://material.io/design/color/
$candy-app-primary: mat-palette($mat-indigo);
$candy-app-accent: mat-palette($mat-pink, A200, A100, A400);
// The warn palette is optional (defaults to red).
$candy-app-warn: mat-palette($mat-red);
// Create the theme object (a Sass map containing all of the palettes).
$candy-app-theme: mat-light-theme($candy-app-primary, $candy-app-accent, $candy-app-warn);
// Include theme styles for core and each component used in your app.
// Alternatively, you can import and @include the theme mixins for each component
// that you are using.
@include angular-material-theme($candy-app-theme);
The most important part of this is to remember that you must include just once the mat-core() in your application (in order to have a single material styles css file).
After that you can create custtom themes by including import '~@angular/material/theming'; wherever desired in the application and apply the theme by wrapping it in a css calss. For example after you include the mat-core once in you root .scss file, in a lazy loaded module you can do the following thing:
@import "~@angular/material/theming";
.theme1 {
$theme-primary: mat-palette($mat-red);
$theme-accent: mat-palette($mat-lime, A200, A100, A400);
// The warn palette is optional (defaults to red).
$theme-warn: mat-palette($mat-red);
// Create the theme object (a Sass map containing all of the palettes).
$theme-theme: mat-light-theme($theme-primary, $theme-accent, $theme-warn);
// Include theme styles for core and each component used in your app.
// Alternatively, you can import and @include the theme mixins for each component
// that you are using.
@include angular-material-theme($theme-theme);
}
<div class="theme1">
<mat-toolbar color="accent">
<button color='primary' mat-button routerLink="/1">Go to 1</button>
<button color='primary' mat-button routerLink="/2">Go to 2</button>
</mat-toolbar>
</div>
Of course instead of two buttons you can also place your router-outlet inside the container with class theme1 and achive the desired result (different theme per lazy loaded module). Keep in mind that we are just importing import '~@angular/material/theming';` in the places where we need custom theming.
Here is a live example: CodeSandbox
