XCFE is the nicest lightweight desktop imho but since my new(no quite so old) thinkpad has more processor/ram, I run plasma now. I like my Plasmoids aka desktop widgets.
The theme is called Card and comes from here, https://www.pling.com/u/phob1an/. Seems to be one of the few people that does the complete package. GTK2, GTK3, Plasma Look & Feel, SSDM login, desktop background pic, Plasma Color Scheme, aurora theme etc etc.