I am mapping the pedestrian crossings in Brussels from Urbis imagery. In JOSM in expert mode, menu, File - From Overpass API - highway = crossing - Build Query - Download.
It would be nice if highway = crossing would be highlighted.
By the way, please criticise my work, I would like that the blind people use it in the year 2020.
When do you want to highlight the crossings ? Before (on the slippy map) or after the download ?
After the download the data behaves just like any other data in JOSM. You could write a mapcss file to "highlight" the crossing.
Right now the crossings are represented by an icon.
Also, with your query you are only downloading the data (typically nodes) mapped as highway crossing, no other data. So you will only see a bunch of nodes in JOSM, not ?
OTOH if you have downloaded an area in JOSM, there is no need to make this query, the data is already there.
I think the order of stylesheets was wrong.