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'));WARNING: If you never add a 'data' event handler, or call resume(), then it'll sit in a paused state forever and never emit 'end'.