[styles] custom theme variables with makeStyles

• This is not a v0.x issue.
• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior 🤔

makeStyles have access to custom variables created in theme https://material-ui.com/customization/themes/#custom-variables

Current Behavior 😯

makeStyles cannot access custom variables created in theme

const useStyles = makeStyles(theme => {
  console.log(theme); // no theme custom variables
  return {
    root: {
      width: '100%',
    },
  };
});

Steps to Reproduce 🕹

Link:

https://codesandbox.io/s/ovjn13pvk9

Your Environment 🌎

Tech	Version
Material-UI	v3.6.0
Material-UI/styles	v3.0.0-alpha.1
React	16.7.0-alpha.2

[eps1lon]

makeStyles is theme agnostic. You actually have to provide a theme via @material-ui/styles/ThemeProvider: https://codesandbox.io/s/zr1mjxxpq4

[PabloDinella]

Can’t find this ‘function as a parameter of makeStyles syntax’ in docs, I only see examples passing an object to makeStyles. Shouldn’t it be noted that makeStyles also accepts a function that will receive the theme, or is it noted somewhere else?