title: Angular Material cant change background color with theme
body: <p>I've been tring to make a custom theme for my site but nothing will effect the background color. This is my theme:</p>
  
  <pre><code>@import '~@angular/material/theming';
  @include mat-core();
  
  $warn: mat-palette($mat-red);
  
  $dark-primary: mat-palette($mat-grey, 900);
  $dark-accent: mat-palette($mat-grey);
  $dark-theme: mat-dark-theme($dark-primary, $dark-accent, $warn);
  @include angular-material-theme($dark-theme);
  
  $blue-primary: mat-palette($mat-indigo, 800, 100, 100);
  $blue-accent: mat-palette($mat-grey, 300, 100, 500);
  $blue-theme: mat-light-theme($blue-primary, $blue-accent, $warn);
  
  .alt-theme {
      @include angular-material-theme($blue-theme);
  }
  </code></pre>
  
  <p>I have <code>mat-app-background</code> on my body but what ever the first included theme is set to dark/light that is what the background color is changed too, black or white.</p>
  
  <p>This was a problem at first but I'm fine with that my issue now is that it doesnt care that the alt-theme is light, the background stays black. Or if the first included theme is light and the alt is dark it will stay white.</p>
  
  <p>EDIT:</p>
  
  <p>So my issue was that I was adding the class to my <code>mat-drawer-container</code> which I guess it doesnt like, I wrapped it in a div and then everything started working as expected</p>