We probably need to add variables in https://github.com/xwiki/xwiki-platform/blob/4245f45c641a2415e1fc99ff187e015803a856f5/xwiki-platform-core/xwiki-platform-web/xwiki-platform-web-war/src/main/webapp/resources/uicomponents/widgets/gallery/gallery.css#L1-L118
We should wait until CSS variables are available to implement this, there's no point in moving everything to LESS to move back.
