While documentation for my "Date Picker Widgets" mini-programming-project is still in the works, and while I plan on putting a bunch of tiny tutorials/whatever videos together ...
Just a preview of an ongoing TiddlyWiki programming mini-project to create some very simple Date Picker Widgets.
There are a few fun elements in there for short "tutorials" about TiddlyWiki (edit-text widgets, macros, filtering, and transclusions), about HTML (elements like tables, divs, and details), and about CSS.
Some good folk have built some excellent "Date Picker" plugins for TiddlyWiki, and these are not substitutes.
Well, unless you are a minimalist and/or a DIY (hobby-programmer?) type.