@mixin bk($class) {
	@if $class == xs {
		@media (max-width: 767px) { @content; }
	}

	@else if $class == sm {
		@media (min-width: 768px) { @content; }
	}

	@else if $class == md {
		@media (min-width: 992px) { @content; }
	}

	@else if $class == lg {
		@media (min-width: 1200px) { @content; }
	}
}

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

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

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