title: Fluent UI React - how to apply global component styles with Fluent ThemeProvider
body: <p>I'm working with the theming code below.  I'm able to apply a global Fluent theme with the ThemeProvider and createTheme utility, but when I add component specific themes, I'm not getting any typings, which makes theming very difficult.</p>
  <p>So <strong>my question is</strong>: how do I apply global component-specific styles using Fluent ThemeProvider with strong typing.</p>
  <p>If, for example, I wanted to add a box shadow to all Fluent PrimaryButtons, I wouldn't know what properties to access on the <code>components</code> key passed into <code>createTheme</code>.</p>
  <p>If you've done any global component theming, please let me know what pattern you used and if I'm on the right track, thanks!</p>
  <pre class="lang-js prettyprint-override"><code>import { createTheme } from '@fluentui/react';
  import { PartialTheme } from '@fluentui/react-theme-provider';
  
  // Trying to add global component styles (not getting typings)
  const customComponentStyles = {
      PrimaryButton: {
          styles: {
              root: {
                  background: 'red'
              }
          }
      }
  };
  
  export const fluentLightTheme: PartialTheme = createTheme({
      components: customComponentStyles, // Want to apply component styles
      palette: {
          themePrimary: '#0078d4',
          themeLighterAlt: '#eff6fc',
          themeLighter: '#deecf9',
          themeLight: '#c7e0f4',
          themeTertiary: '#71afe5',
          themeSecondary: '#2b88d8',
          themeDarkAlt: '#106ebe',
          themeDark: '#005a9e',
          themeDarker: '#004578',
          neutralLighterAlt: '#faf9f8',
          neutralLighter: '#f3f2f1',
          neutralLight: '#edebe9',
          neutralQuaternaryAlt: '#e1dfdd',
          neutralQuaternary: '#d0d0d0',
          neutralTertiaryAlt: '#c8c6c4',
          neutralTertiary: '#a19f9d',
          neutralSecondary: '#605e5c',
          neutralPrimaryAlt: '#3b3a39',
          neutralPrimary: '#323130',
          neutralDark: '#201f1e',
          black: '#000000',
          white: '#ffffff'
      }
  });
  </code></pre>