So I achieved this with a Theme Component.
Unfortunately this presently will have to be added to your designated “Dark Theme” and will not switch automatically with a user’s “Dark Mode”.
Nonetheless it’s useful progress to build upon:
:root {
--map-tiles-filter: brightness(0.6) invert(1) contrast(3) hue-rotate(200deg) saturate(0.3) brightness(0.7);
}
.locations-map {
.leaflet-tile-pane {
filter:var(--map-tiles-filter, none);
}
.leaflet-marker-shadow {
display: none;
}
}