title: How can I customize material-ui V1 components across entire application when creating a theme?
body: <p>in material-ui v0, when creating a theme with <code>const muiThemeV0 = getMuiTheme(theme);</code>
  i can simply add a property to the themeOptions for each component based on this file:
  <a href="https://github.com/mui-org/material-ui/blob/master/src/styles/getMuiTheme.js" rel="nofollow noreferrer">https://github.com/mui-org/material-ui/blob/master/src/styles/getMuiTheme.js</a> (currently on the master branch when writing this question), and can customize not only colors but the theme border-radius etc, and specific components sizes and colors.
  for example: </p>
  
  <pre><code>const theme = {
    slider: {
      selectionColor:  colors.primary1Color,
      handleFillColor: colors.primary1Color,
      trackSize:       6,
    }
  }
  </code></pre>
  
  <p>I tried going through the <a href="https://material-ui-next.com/customization/overrides/" rel="nofollow noreferrer">https://material-ui-next.com/customization/overrides/</a> docs, but can't see examples and/or a list of options in the source code like MUI-v0 when i want to use <code>const muiThemeV1 = createMuiTheme(theme);</code>
  are there any docs for this kind of customization in v1?
  is this even possible?</p>