Angular custom style to mat-dialog

You can pass a custom panelClass in your matDialogConfig Object (doc here)

so

openErrorDialog(errore: string): void{
    let dialogRef = this.dialog.open(ErrorDialog, {
        width: '80%',
        data: { error: errore }
        panelClass: 'custom-modalbox'
    });
}

And in your custom panelClass you can override the padding :

.custom-modalbox {
    mat-dialog-container {
        padding: 0;
    }
}

But your .custom-modalbox should be global scoped to be applied (not defined in the component styles )