Cross browser border-radius SASS mixin with varargs

Few days ago I needed to create style sheets with many rounded boxes, where different corners had to be rounded differently (think about Bootstrap’s button groups).

CSS has this nifty shorthand to specify border width in one line, like with border-width: 1px 2px 3px 4px, but it lacks the same for border-radius. So I decided to create something similar using Sass mixins with dynamic parameters. Another nice feature you get using the border-width shorthand is that you can specify less than four parameters, and the values will be applied on different sides of your box, so in the end all side will have the whole border-width set.

I wanted to achieve the same for my border-radius mixin, although I could not start specifically with the top side. I decided to go with the top right corner for the first parameter, while trying to keep a sane repeating pattern. Here is the result:

=border-width($t, $r: $t, $b: $t, $l: $r)
  border-top-width: $t
  border-right-width: $r
  border-bottom-width: $b
  border-left-width: $l

  border-top-right-radius: $value
  -moz-border-top-right-radius: $value
  -webkit-border-top-right-radius: $value

  border-top-left-radius: $value
  -moz-border-top-left-radius: $value
  -webkit-border-top-left-radius: $value

  border-bottom-right-radius: $value
  -moz-border-bottom-right-radius: $value
  -webkit-border-bottom-right-radius: $value

  border-bottom-left-radius: $value
  -moz-border-bottom-left-radius: $value
  -webkit-border-bottom-left-radius: $value

=border-radius($tr, $br: $tr, $bl: $br, $tl: $tr)