Use icon-dropshadow for app icon
See https://gnome.pages.gitlab.gnome.org/libadwaita/doc/main/style-classes.html#app-icons.
The class welcome-image is not in style.css.
See https://gnome.pages.gitlab.gnome.org/libadwaita/doc/main/style-classes.html#app-icons.
The class welcome-image is not in style.css.