Bug: Image thumbnails display

[lbesson]

Describe the bug
Vertical images inserted into documents are often too big and blurry

Screenshots
Example 1 (https://www.camptocamp.org/routes/53823/fr/tete-des-fetoules-arete-w):

Example 2 (https://www.camptocamp.org/articles/269090/fr/les-coinceurs-protections-actives-coinceurs-mecaniques):

Additional context
Current css is:

figure[c2c\:size='MI'] {
  width: 25vw;
  max-width: 400px;
  img {
    width: 25vw;
    max-width: 400px;
  }
}

I don't know the reasoning behind (maybe some kind of mix between not too blurry, but still be 'big enough' one the page), but IMHO, we should have the same max-width and max-height.
Current state is well for horizontal images, but bad for vertical ones

[lbesson]

maybe something like

max-width: 400px;
max-height: 400px;
max-width: min(400px, 25vw);
max-height: min(400px, 25vw);

(the two first lines acting as fallback for browsers that don't support min())