Using #OpenLayers and #CSS filters to style #OSM #WebMaps in your application into greyscale, dark mode and more. Some note and sample filters at:
https://notepad.onghu.com/2024/open-layers-greyscale-maps-more-with-css-filters/
@onghu exiting feature of #openlayers I did not know of
@jakobmiksch
Actually, more like a web feature - but well supported from within Openlayers