@leocg Well the yellow button happears with "installe" written(im in French so perhaps "installing" in english) and then after a few time the green button happears with "installed" written. And... i just noticed where it come from, i think this problem was due to the update of opera that i made, but after restarting my pc the problem is gone and i can install wallpapers normally and with no problems, so yeah i guess that this post was a bit useless, and i apologize for having unnecessarily monopolized the staff of Opera. I wish you a great day.