css - 无法在 Vaadin 自定义主题中设置字体大小和背景图像

Question

我在 Vaadin 的 valo 主题之上定义了我自己的自定义主题。

这是文件 mycustomtheme.scss 的内容：

 //this line works, it sets the background-color of the app to light-blue:
 $v-background-color: hsl(192°, 61%, 51%);

 //the following line is supposed to set the font-color in the app to white but has no effect, the font-color in the app is still black: 
 $v-font-color: rgb(255, 255, 255);

 @import "../valo/valo.scss";


 @mixin mycustomtheme {

     @include valo;

    //the following 3 lines don't have any effect either. The background-image does not get displayed: 
    .defaultView {
        background-image: url("urlOf/Image");
    }
}

要设置背景图像的组件的 java 代码是：

    //other code ...
    gridLayout = new GridLayout(4,2);
    gridLayout.setSizeFull();
    gridLayout.addStyleName("defaultView");
    addComponent(gridLayout);
    //more code ...

1.) 为什么将背景颜色设置为蓝色有效，但将字体颜色设置为白色无效？我对照 Vaadin 团队的示例检查了我的代码，我看不出我可能做错了什么：

https://vaadin.com/docs/v8/framework/articles/ValoExamples.html

2.) 为什么不显示背景图像？