This technique could be accomplished with all sorts of themes. I am partial to eucalyptus leaves as well as palm fronds both of which would work well. The stickers look like they were made with washi paper. It’s delicate but the colors are slightly muted and could easily be matched to fountain pen ink.
On Amazon, I found a camellia and an azalea made by the same company as the washi in the video, plus a set of black, white, and gold stickers that looks promising.
Have you ever done something like this? How did it turn out?