CSS styling the HTML representation of InferenceData

We use `` to enclose the plaintext representation of the groups in the custom `InferenceData` HTML `show` method. By default, the group name is styled with the right-facing arrow to the far left, which rotates to point down when the group is expanded. However, the CSS of the page in which the `InferenceData`'s HTML is inserted might custom style the `` to remove the arrow. Jupyter does this, for example.

We should embed whatever CSS is necessary in a `` block after the HTML to ensure that at least in Jupyter the arrow is shown correctly, but it's better if we can style the `<details>` to show the error no matter what the global CSS is.

Related, each of our tags should probably have a custom class associated with it, which would allow others to style our HTML as they prefer.