[Clock/Calendar] Always show current date

[donovanglover]

Is your feature request related to a problem? Please describe.
It would be nice if there was a way to always highlight the current date. Currently if you click another date the current date doesn't have any sort of indicator.

Describe the solution you'd like
Ability to style dates with CSS. Might already be possible? https://docs.gtk.org/gtk4/class.Calendar.html#css-nodes

Describe alternatives you've considered
Could make clicking on the header select the current year/month/day. Would be useful when looking at dates from a few months before.

Could also select the current date again when the calendar popup is opened/closed instead of persisting state.

[A-Cloud-Ninja]

This and other similar issues (#245 comes to mind) are probably better suited for after #112 is resolved unfortunately. It doesn't seem that Gtk3 exposes CSS nodes for calendar dates like Gtk4 does, which is what your link is referencing. Doing this in a custom manner would probably be a lot of work for more than just styling "today", which Gtk4 exposes out of the box on the widget, without code doing anything special with it.