SCSS mixins for cross browser CSS3 border-radius, transition, gradient, and box shadow

mixins.scss

//Cross browser CSS3 mixins

@mixin box-shadow($left, $top, $radius, $color) {
	box-shadow: $left $top $radius $color;
	-webkit-box-shadow: $left $top $radius $color;
	-moz-box-shadow: $left $top $radius $color;
}

@mixin transition($property, $duration, $easing: linear) {
	transition: $property $duration $easing;
	-webkit-transition: $property $duration $easing;
	-moz-transition: $property $duration $easing;
}

@mixin border-radius($radius) {
	border-radius: $radius;
	-webkit-border-radius: $radius;
	-moz-border-radius: $radius;
}

@mixin border-radii($topleft, $topright, $bottomright, $bottomleft) {
	border-top-left-radius: $topleft;
	border-top-right-radius: $topright;
	border-bottom-right-radius: $bottomright;
	border-bottom-left-radius: $bottomleft;
	-webkit-border-top-left-radius: $topleft;
	-webkit-border-top-right-radius: $topright;
	-webkit-border-bottom-right-radius: $bottomright;
	-webkit-border-bottom-left-radius: $bottomleft;
	-moz-border-radius-topleft: $topleft;
	-moz-border-radius-topright: $topright;
	-moz-border-radius-bottomright: $bottomright;
	-moz-border-radius-bottomleft: $bottomleft;
}

@mixin gradient($color1, $color2) {
	background-color: $color1;
	filter: progid:DXImageTransform.Microsoft.gradient(GradientType=0, startColorstr=#{$color1}, endColorstr=#{$color2});
	background-image: -moz-linear-gradient(center top, $color1, $color2);
	background-image: -webkit-gradient(linear, 0% 0%, 0% 100%, from($color1), to($color2));
}

I used it like this: @include border-radii(0, 0, 5px, 5px);.
I get this error: Error: Mixin border-radii missing argument $topright..

Why does this happen?

You have to use "Null" instead of "0"

@mixin border-radii($topleft: null, $topright: null, $bottomright: null, $bottomleft: null) {
  @if $topleft != null and $topleft >= 0 {
    border-top-left-radius: $topleft;;
    -webkit-border-top-left-radius: $topleft;
    -moz-border-radius-topleft: $topleft;
  }

  @if $topright != null and $topright >= 0 {
    border-top-right-radius: $topright;
    -webkit-border-top-right-radius: $topright;
    -moz-border-radius-topright: $topright;
  }

  @if $bottomleft != null and $bottomleft >= 0 {
    border-bottom-left-radius: $bottomleft;
    -webkit-border-bottom-left-radius: $bottomleft;
    -moz-border-radius-bottomleft: $bottomleft;
  }

  @if $bottomright != null and $bottomright >= 0 {
    border-bottom-right-radius: $bottomright;
    -webkit-border-bottom-right-radius: $bottomright;
    -moz-border-radius-bottomright: $bottomright;
  }
}

you can also do like this right?

@mixin border-radius($top-left:null, $top-right:null, $bottom-right:null, $bottom-left:null){
  -webkit-border-radius: $top-left $top-right $bottom-right $bottom-left;
  -moz-border-radius: $top-left $top-right $bottom-right $bottom-left;
  -ms-border-radius: $top-left $top-right $bottom-right $bottom-left;
  border-radius: $top-left $top-right $bottom-right $bottom-left;
}