node_modules/@angular/material/sidenav/_sidenav-theme.scss

@import '../core/style/private';
@import '../core/theming/palette';
@import '../core/theming/theming';

@mixin mat-sidenav-color($config-or-theme) {
  $config: mat-get-color-config($config-or-theme);
  $primary: map-get($config, primary);
  $accent: map-get($config, accent);
  $warn: map-get($config, warn);
  $background: map-get($config, background);
  $foreground: map-get($config, foreground);

  $drawer-background-color: mat-color($background, dialog);
  $drawer-container-background-color:  mat-color($background, background);
  $drawer-push-background-color: mat-color($background, dialog);
  $drawer-side-border: solid 1px mat-color($foreground, divider);

  .mat-drawer-container {
    background-color: $drawer-container-background-color;
    color: mat-color($foreground, text);
  }

  .mat-drawer {
    background-color: $drawer-background-color;
    color: mat-color($foreground, text);

    &.mat-drawer-push {
      background-color: $drawer-push-background-color;
    }

    &:not(.mat-drawer-side) {
      // The elevation of z-16 is noted in the design specifications.
      // See https://material.io/design/components/navigation-drawer.html
      @include mat-private-theme-elevation(16, $config);
    }
  }

  .mat-drawer-side {
    border-right: $drawer-side-border;

    &.mat-drawer-end {
      border-left: $drawer-side-border;
      border-right: none;
    }
  }

  [dir='rtl'] .mat-drawer-side {
    border-left: $drawer-side-border;
    border-right: none;

    &.mat-drawer-end {
      border-left: none;
      border-right: $drawer-side-border;
    }
  }

  .mat-drawer-backdrop.mat-drawer-shown {
    $opacity: 0.6;
    $backdrop-color: mat-color($background, card, $opacity);

    @if (type-of($backdrop-color) == color) {
      // We use invert() here to have the darken the background color expected to be used. If the
      // background is light, we use a dark backdrop. If the background is dark,
      // we use a light backdrop.
      background-color: invert($backdrop-color);
    }
    @else {
      // If we couldn't resolve the backdrop color to a color value, fall back to using
      // `opacity` to make it opaque since its end value could be a solid color.
      background-color: $backdrop-color;
      opacity: $opacity;
    }
  }
}

@mixin mat-sidenav-typography($config-or-theme) {}

@mixin _mat-sidenav-density($config-or-theme) {}

@mixin mat-sidenav-theme($theme-or-color-config) {
  $theme: mat-private-legacy-get-theme($theme-or-color-config);
  @include mat-private-check-duplicate-theme-styles($theme, 'mat-sidenav') {
    $color: mat-get-color-config($theme);
    $density: mat-get-density-config($theme);
    $typography: mat-get-typography-config($theme);

    @if $color != null {
      @include mat-sidenav-color($color);
    }
    @if $density != null {
      @include _mat-sidenav-density($density);
    }
    @if $typography != null {
      @include mat-sidenav-typography($typography);
    }
  }
}