Harmonize spacing around figures and section titles

[Bisaloo]

@CarmenTamayo reported that we are not consistent across vignettes and packages in the space around figures and section titles.

Rather than requiring authors to manually adjust the spacing in each vignette, we should solve this globally here via CSS.

Solving this issue will likely by done through a co-working session with @CarmenTamayo.

[CarmenTamayo]

Hi Hugo, thank you for raising this point, could I ask what this co-working session would entail?
Thank you

[Bisaloo]

Basically, jump on a call with you and adjust the CSS live with you so you can help decide what looks good.

An alternative approach would be for you to take a screenshot of any vignette, manually edit it via an image editing tool to show what good would look like, and then I can translate it to CSS here on my own.