White iframe, before content is loaded

[chrisjsewell]

The first time an iframe is loaded (subsequently it appears cached), and if the documentation is being hosted online (i.e. longer load page times), it can show an empty, white iframe before the content is loaded.

Ideally this would look nicer, e.g. the preview modal would not how, until the source is loaded or something

On Firefox (OSX), but same seen on Chrome:

[chrisjsewell]

Partially fixed in #7, although still seems to be an issue in seom browsers, i.e. stills shows white at start sometimes 🤷