[Select] [Styling Bug] Specifying root class key inside inputProps prop removes default styling

[franklixuefei]

• This is a v1.x issue (v0.x is no longer maintained).
• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior

specifying root class key inside inputProps prop should not remove the default styling.

Current Behavior

Suppose I have a style like this:

const style = theme => ({
  input: {
    width: '100%'
  }
});

And then, I have a component that renders a Select component:

<Select
  value="and"
  inputProps={{
    classes:{ root: classes.input }
  }}
>
  <MenuItem value={"and"}>And</MenuItem>
  <MenuItem value={"or"}>Or</MenuItem>
</Select>

This results in the default styling being removed, as shown below:

Before adding style:

After adding style:

Your Environment

Tech	Version
Material-UI	v1.2.1
React	16.4.0
browser
etc

[oliviertassinari]

@franklixuefei Right, we need to merge the classes property in:
https://github.com/mui-org/material-ui/blob/7a412df351bbec25957215a27e94250f49f5e142/packages/material-ui/src/Select/Select.js#L46-L65