Fix some styling issue in extended tooltip

I think it's probably because if this file https://github.com/geoadmin/mf-chsdi3/blob/2e1afa4a680b831599117e6255dcfd8d5c491185/chsdi/static/css/blueimp-gallery-2.11.0.css, which has an 'img' path. Not sure if this is still needed.