only_light/only_dark classes break alignment of images within figures

[idryzhov]

When I use :class: only_light or :class: only_dark on a figure, the image within the figure is left-aligned although it should be centered.
As I understand, this happens because the display: block !important property is added to such images. The property was removed in b414d2f and later was brought back in 3bcbe2c. There's no comment in the linked commits about the necessity of this property, so my question here – why do we need this property and is there any other property that we can use there that won't break the alignment?

[pradyunsg]

Hi there! Could you provide a reproducer for the issue you're seeing?

[idryzhov]

Hi! Thanks for a quick reply.

It's pretty simple. When I use:

.. figure:: https://source.unsplash.com/200x200/daily?cute+dogs
    :class: only_light

.. figure:: https://source.unsplash.com/200x200/daily?cute+cats
    :class: only_dark

The image is left-aligned:

However, I expect it to be centered, as with regular figure, when I don't use only-light/only-dark classes:

[idryzhov]

@pradyunsg hi again!

Actually, I think I found the right solution.
When using figures, one must use :figclass: only_light/dark instead of :class: only_light/dark.
This way, the class applies to the <figure> HTML tag instead of the <img> and the image is aligned correctly.
More than that, it allows to use different captions depending on the light/dark mode:

.. figure:: https://source.unsplash.com/200x200/daily?cute+dogs
    :figclass: only_light
    :align: center

    Dog

.. figure:: https://source.unsplash.com/200x200/daily?cute+cats
    :figclass: only_dark
    :align: center

    Cat

So there's no issue with the Furo theme, sorry. However, the usage of :figclass: only_light/dark for figures may be worth noting in the docs :)

[pradyunsg]

I've gone ahead and documented this as well.