I can't think of a reason why limiting the border to a maximum
would make any sense.
The original intention was probably to set a minimum border width
to avoid having to deal with border/no-border complexity in the code,
but as cairo accepts a line width of 0, it just works.
However limiting the size to the overall height seems reasonable,
as at that size a bigger height and different fill color can
achieve the same effect without requires special handling of
other values like the radius.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2994>
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