SASS cross browser rounded corner mixins

SASS_rouded_corner_mixins.sass

$default_rounded_amount: 5px
// Round corner at position by amount.
@mixin round-corner($position, $amount: $default_rounded_amount)
  border-#{$position}-radius: $amount
  -webkit-border-#{$position}-radius: $amount

@mixin round-corner-mozilla($position, $amount: $default_rounded_amount)
  -moz-border-radius-#{$position}: $amount

// Round left corners by amount
@mixin round-left-corners($amount: $default_rounded_amount)
  @include round-corner("top-left", $amount)
  @include round-corner("bottom-left", $amount)
  @include round-corner-mozilla("topleft", $amount)
  @include round-corner-mozilla("bottomleft", $amount)

// Round right corners by amount
@mixin round-right-corners($amount: $default_rounded_amount)
  @include round-corner("top-right", $amount)
  @include round-corner("bottom-right", $amount)
  @include round-corner-mozilla("topright", $amount)
  @include round-corner-mozilla("bottomright", $amount)

// Round top corners by amount
@mixin round-top-corners($amount: 5px)
  @include round-corner("top-left", $amount)
  @include round-corner("top-right", $amount)
  @include round-corner-mozilla("topleft", $amount)
  @include round-corner-mozilla("topright", $amount)

// Round bottom corners by amount
@mixin round-bottom-corners($amount: $default_rounded_amount)
  @include round-corner("bottom-left", $amount)
  @include round-corner("bottom-right", $amount)
  @include round-corner-mozilla("bottomleft", $amount)
  @include round-corner-mozilla("bottomright", $amount)

// Round all corners by amount
@mixin round-corners($amount: $default_rounded_amount)
  border-radius: $amount
  -moz-border-radius: $amount
  -webkit-border-radius: $amount

Great guide! I just found this that may help the box-shadow

@mixin box-shadow($top, $left, $blur, $color, $inset:"") {
  -webkit-box-shadow:$top $left $blur $color #{$inset};
  -moz-box-shadow:$top $left $blur $color #{$inset};
  box-shadow:$top $left $blur $color #{$inset};
}

http://stackoverflow.com/questions/3525007/making-a-sass-mixin-with-optional-arguments