Fix for docments table column widths

Because [Markdown tables must have fixed-width columns](https://github.com/quarto-dev/quarto-cli/discussions/7399), the layout of the docments table is less than ideal. Here's an example from the nbdev documentation:

We can use a css rule in styles.css to get auto spacing back:

```.table colgroup col {width: auto !important;} ```

That looks a lot nicer to me:

If it's too heavy-handed to disable all `colgroup` width specifications, maybe we could add a custom class to the docment table and use that in the css rule?

Start by locating styles.css and the CSS for the docments table, then compare the generated table layout with the examples in the issue. Decide whether the width rule should apply broadly or through a custom table class. Done means the docments table has automatically spaced columns without adversely affecting unrelated tables.

Written by the indexing model from the issue text.