Захар Морозов

<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">

$ git clone https://github.com/ilyar/bem-test.git && cd bem-test && npm i
$ gulp
[14:19:01] Using gulpfile ~/lab/bem-test/gulpfile.js
[14:19:01] Starting 'default'...
[14:19:01] Finished 'default' after 146 ms
$ cat dist/index.css 
.menu {
	list-style: none;
	color: green;
}

.menu__item {
	margin-left: 10px;
}

var gulp    = require('gulp');
var bem     = require('gulp-bem');
var concat  = require('gulp-concat');
 
var levels = ['base', 'blocks'];
var tree = bem(levels);
 
tree.deps('blocks/page')
    .pipe(bem.src('{bem}.css'))
    .pipe(concat('index.css'))
    .pipe(gulp.dest('./dist'));