trbl

Expand component arrays to [top, right, bottom, left], in accordance with CSS rules. That is:

[a] => [a, a, a, a]
[a, b] => [a, b, a, b]
[a, b, c] => [a, b, c, b]
[a, b, c, d] => [a, b, c, d]

For convenience, a scalar argument is also supported:

a => [(int)a, (int)a, (int)a, (int)a]