Markdown paragraphs are not centered vertically when rendered

[JasonWeill]

Description

Markdown paragraphs are not centered vertically when rendered. To fix we would need to be careful about spacing.

(found by @ellisonbg)

Context

• Operating System and version: macOS
• Browser and version: Firefox
• JupyterLab version: 4.0.0a37

[fcollonval]

Indeed this requires to be careful. For instance what is happening when there are two paragraphs.

To fix this, I would suggest looking at the reason for the input cell to be larger than the text (I guess this is conditioned by the toolbar height). Adding a top margin or padding sounds not like a good approach as it will reduce the vertical space available for content going against the lengthy discussion we already had when introducing the cell toolbar.