将Angular素材升级到版本6后的版式配置问题

在将角形材料更新到版本6之后，所有标题元素（h1-h6）都没有获得正确的字体系列和字体大小。

这是我的自定义配置：

$custom-typography: mat-typography-config(
    $font-family: 'Roboto, sans-serif',
    // Large, one-off headers, usually at the top of the page.
    $display-4:     mat-typography-level(112px, 112px, 300),
    $display-3:     mat-typography-level(56px, 56px, 400),
    $display-2:     mat-typography-level(45px, 48px, 400),
    $display-1:     mat-typography-level(34px, 40px, 400),
    // h1
    $headline:      mat-typography-level(24px, 32px, 400),
    // h2
    $title:         mat-typography-level(20px, 32px, 500),
    // h3
    $subheading-2:  mat-typography-level(16px, 28px, 400),
    // h4
    $subheading-1:  mat-typography-level(15px, 24px, 400),
    // Bolder body text.
    $body-2:        mat-typography-level(14px, 24px, 500),
    // Base body text.
    $body-1:        mat-typography-level(18px, 20px, 400),
    // Smaller body and hint text.
    $caption:       mat-typography-level(12px, 20px, 400),
    // Buttons and anchors.
    $button:        mat-typography-level(18px, 14px, 300),
    // Line-height must be unit-less fraction of the font-size.
    $input:         mat-typography-level(18px, 1.2, 300)
);

@include mat-core($custom-typography);