SCSS: mixins gradient forbutton

gradient.scss

@mixin btn_gradient($color: #9D9D9D, $width: 200px, $height: 50px){
	width: $width;
	height: $height;
	background: $color;
	background: -moz-linear-gradient(top,  lighten($color, 25%) 0%, $color 50%, lighten($color, 25%) 100%);
	background: -webkit-linear-gradient(top,  lighten($color, 25%) 0%,$color 50%,lighten($color, 25%) 100%);
	background: linear-gradient(to bottom,  lighten($color, 25%) 0%,$color 50%,lighten($color, 25%) 100%);
	filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='$color', endColorstr='$color',GradientType=0 );
	display: inline-block;
	cursor: pointer;
	font-size: $height * 0.5;
	line-height: $height;
	text-transform: uppercase;
	text-align: center;
	border-radius: $height * 0.1;
	box-shadow: 0px 0px $height * 0.1 darken($color, 10%);
	&:hover{
		background: $color;
		background: -moz-linear-gradient(top,  lighten($color, 10%) 0%, lighten($color, 25%) 50%, lighten($color, 10%) 100%);
		background: -webkit-linear-gradient(top,  lighten($color, 10%) 0%, lighten($color, 25%) 50%, lighten($color, 10%) 100%);
		background: linear-gradient(to bottom,  lighten($color, 10%) 0%, lighten($color, 25%) 50%, lighten($color, 10%) 100%);
		filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='$color', endColorstr='$color',GradientType=0 );
	}
}