title: Transparent background in angular material dialog
body: <p>I am trying to change the color of the angular material dialog using css var (), but instead of the color I need, the background becomes transparent.</p>
  
  <p>Css style:</p>
  
  <pre><code>.custom-dialog &gt;  mat-dialog-container {
    background: var(--background);
  }
  </code></pre>
  
  <p>Open dialog function: </p>
  
  <pre><code>openDialogForCreateDirectory(): void {
      this.dialog.open(CreateDirectoryComponent, {
        width: '400px',
        panelClass: 'custom-dialog'
      });
    }
  </code></pre>