bem.scss

@mixin module($name) {
  .#{$name} {
    @at-root {
      @content;
    }
  }
}

@include module("nav") {

	#{&}-list {
		outline: 1px solid orange;
		height: 400px;
	}

	#{&}-item {
		background: red;
		height: 20px;
		margin-bottom: 10px;			
		&.active {
			background: blue;
		}
	}

}