styled-components support

When previewing a file in the collapsible tree view, my `styled-components` code:

```js
const ActionText = styled.button`
${props => props.theme.ActionText(props.theme)[props.variant]};
`;
```

displays like this:
```js
const ActionText = styled.button`
___CSS_0___;
`;
```

Start by reproducing the example in the collapsible tree view's file preview and trace where styled-components template contents are transformed. Compare the displayed preview with the original snippet; done means the interpolated expression is preserved instead of being replaced by ___CSS_0___.

Written by the indexing model from the issue text.