I adapted it into a minimal CSS snippet.
The original didn’t work in preview mode, and this does.
.theme-dark img[alt$="invert_dark"] {
filter: invert(1);
}
.theme-light img[alt$="#invert_light"] {
filter: invert(1);
}
Usage:
![[dark_image.png#invert_dark]]
![[light_image.png#invert_light]]