Compatible issue in global-styles setting

[PitterL]

In global-styles, there set the app CSS with:

  #app {
    background-color: #fafafa;
    min-height: 100%;
    min-width: 100%;
  }

There set the background-color with a near white color, but hard to be aware of this.
Suggest to comment it which conflicted with some UI.

Referred following issue:
myxvisual/react-uwp#75 (comment)