角度材质6 - 更改主题后，某些组件的背景显示为透明

Question

在自定义材质角度主题时，select，dialog和snackbar等组件的背景显得透明，我的sass代码为：

@import '../../node_modules/@angular/material/theming';
@include mat-core();

$default-app-primary: mat-palette($mat-cyan, 700);
$default-app-accent:  mat-palette($mat-green, 600, A100, A400);
$default-app-warn:    mat-palette($mat-red, 700);

$default-app-theme: mat-light-theme($default-app-primary, $default-app-accent, $default-app-warn);
$no-login-app-theme: mat-dark-theme($default-app-primary, $default-app-accent, $default-app-warn);

$custom-typography: mat-typography-config(
  $font-family: 'Montserrat, sans-serif'
);

@include angular-material-typography($custom-typography);
@include angular-material-theme($default-app-theme);

提前致谢