Describe the bug

context
When I switch to dark mode, the output cells have borders which is not what I see in light mode.

expectation
I expected dark mode to have borderless output cells similar to what I see in light mode.

bug
But instead I see bordered output cells in dark mode that visually clash with input cells that also have borders.

problem
This is a problem for people scanning a long notebook with alternating input and output cells because there's very little visual distinction between input and output cells (except the green left border). Also a little UX note: the borders are used to draw more visual attention, the input cells are already doing that, output cells don't need to, esp when notebook has a lot of them.

Reproduce the bug

1. Go to https://myst-nb.readthedocs.io/en/latest/authoring/jupyter-notebooks.html#code-cells-and-outputs
2. Note how the output cell looks borderless and is immediately distinguishable from two inputs cells sandwiching it.

3. Switch to dark mode.
4. Note how the output cell looks bordered and is hard to distinguish from two input cells sandwiching it (it becomes more apparent in long notebooks with no narrative text but alternating input and output cells)

List your environment

same as what docs build is using