Bootstrap Lite subtheme and Leaflet map icon problem (solved)

I'm using Leaflet to display maps from geofield data, with the great Leaflet Widget for Geofield module and I was having trouble with the accurate display of the marker points. When editing, the marker position displayed correctly but shown displayed on the node display (or in Views) the marker was consistently too high, by about 20 pixels.

I struggled with this issue and wasted a few hours but with help (from 'indigoxela' and 'yorkshire-pudding' in https://backdrop.zulipchat.com/) managed to get to the bottom of it.

I had built a subtheme of Bootstrap Lite, and that theme adds a top and bottom margin of 20px to the marker (img).

I added to my subtheme's styles.css:

img {
margin: 0;
}

and all was displayed perfectly.

I'm adding this here in case anyone else comes across this particular combination of theme and module and sees the same problem.