That border-1 is missing is an inconsistency.

[olafurw]

border-2 is border-width: 2px;
and
border is border-width: 1px;
but there is no border-1

And initially I thought this was a pattern that followed some consistent internal naming system.
But it's not:

• There is outline-1 and outline-2 (and outline is to make the line solid)
• There is ring-1 and ring-2 (and ring is ring-3)
• There is stroke-1 and stroke-2 (and no stroke)

So can we please get border-1 that means border-width: 1px;