title: Material-UI for React: cannot see changes when applying <ThemeProvider>
body: <p>I cannot see any change when applying "ThemeProvider" tag, even in a simple project as shown below.
  There is no errors/warnings in the browser console (except for unused imports, but it fails even if I remove them all).</p>
  
  <pre><code>import React, { Component } from "react";
  import Grid from "@material-ui/core/Grid";
  import CssBaseline from "@material-ui/core/CssBaseline";
  import MainBar from "./modules/MainBar";
  import MainTemplate from "./style/MainTemplate";
  import Palette from "./palette";
  import { Button } from "@material-ui/core";
  import { createMuiTheme } from "@material-ui/core/styles";
  import { ThemeProvider } from "@material-ui/styles";
  import purple from '@material-ui/core/colors/purple';
  
  
  const theme = createMuiTheme({
    typography: {
      useNextVariants: true
    },
    palette: {
      primary: purple,
      secondary: {
        main: "#f44336"
      }    
    }
  });
  
  class App extends Component {
    render() {
      return (
        &lt;div className="App"&gt;
          &lt;ThemeProvider theme={theme}&gt;
            &lt;Button color="primary"&gt;BUTTON&lt;/Button&gt;
          &lt;/ThemeProvider&gt;
        &lt;/div&gt;
      );
    }
  }
  
  export default App;
  </code></pre>
  
  <p>Any idea about it? Its almost like documentation example, and it doesn't work.
  Thank you.</p>