Setting Chart Themes 

Hi,

My apologies if this isn't the right place to ask but how would I go about setting the theme? i.e) 
fig.layout.template = 'plotly_dark' .

I've tried setting up my layout config as follows:

```
,
    layout: {
      template: "plotly_dark",
      dragmode: "zoom",
      ......
```

Regards