Show variations as buttons

Hi !
I’ve configured an attribute so that the variations appear as buttons (swatch style #4, disabled swatch style #3, swatch size M). However, by default, we can’t customize the appearance of these buttons. They have a light gray outline, and when hovered, they switch to a black background with white font.
Is there an option to customize the display of variations as buttons?
Or do we have to customize the CSS?
If we have to customize the CSS, could you please provide an example of CSS code to achieve the same look as the example on the site I’m sending you ?
Thanks in advance!