Change Paper borderColor in material-ui React?

I’m using React with Material-UI and trying to customize the Paper component to have a green border color. I’ve tried the following code:

       style={{ padding: 50, }}
       variant="outlined" square={true}
          root: classes.root, // class name, e.g. `classes-nesting-root-x`
       This paper component                     

With the following customization style:

root: {
        borderRadius: 20,
        borderColor: '#000'

The borderRadius property is working fine, but the borderColor property is not working. Does anyone have any suggestions?

root: {
        borderRadius: 20,
        border: '2px solid green'

Use the border property instead of borderColor to specify the border color and width.