Thanks to Tirifto for his
sage advice (linguistically, stylistically, and generally); and for his
website-generator, Pageling, with which I generate this site. Praised be!
And an additional thanks to Tirifto for the flags of Esperanto and the UK, which are used for language-selection at the post-list. They come from his impressively large and cohesive flags emoji-pack made for fediverse, which is mostly under the CC0.
The rose corner-ornament and divider ornament can be found at OpenVerse and Flickr, uploaded by CircaSassy in 2011. They apparently come from a specific book archived on the Internet Archive, “Desk book of type specimens, borders, ornaments, brass rules and cuts: catalogue of printing machinery and printers' supplies”. As the book is so old, these borders are under the public domain, barring the edits of CircaSassy; which are under the CC BY 2.0.
The drawing of Nagato Yuki used in the corner-ornament of the Post-list is from an unknown artist. The original source seems to be here, according to SauceNao (though the page is dead, now). If you find the author, do tell!