Why 300px min-width for :root?

This is an issue to discuss why

https://gitlab.postmarketos.org/postmarketOS/mobile-config-firefox/-/blob/master/src/userChrome/root.css?ref_type=heads#L6

is set to 300px.

I am opening this because I brought it up in an discussion with regard to upstreaming, because I remembered that while fixing #63 (closed) I had noticed that setting the width to 360px (the actual device screen width in logical pixels) made the date-picker work okay without the fix I added in !45 (merged).

What needs investigation (IMHO):

• Without the change from !45 (merged), and with https://gitlab.postmarketos.org/postmarketOS/mobile-config-firefox/-/blob/master/src/userChrome/root.css?ref_type=heads#L6 changed to 360px, how does the date picker behave on a device with a width of more than 360 logical pixels (e.g., Fairphone 5 set to 300% scaling or any other device at some fractional scaling value that achieves this)? (https://gitlab.postmarketos.org/1peter10/mobile-config-firefox/-/tree/experiment/minimal-userchrome may work for evaluating this)
• What other fixes can we drop with setting the min-width to 360px (or actual device width, if that is possible in a generic way or via a (custom) about:config value (see !56 (merged) for the basic idea and limitations))?
• ...