preview doesn't apply css of root view

Hello,

I have created a 2D app assigned the class "main" to the root view "Home" and put

.main {
  background-color: #242730;
  text-align: center;
  color: white;
}

in my css. Now, the editor applies that correctly, but the preview ignores it. Is that a bug or am i doing something wrong?

I tried it both in firefox and chrome