css - gulp-uncss error: unable to parse: -

having problem running gulp-uncss rid of unused code. mistake seems parsing of css.

c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\bluebird\js\release\async.js:48         fn = function () { throw arg; };                            ^  error: uncss/node_modules/css: unable parse undefined: missing '{' near line 34:1         29:        @import "components/_navbar";         30:        @import "components/_slick";         31:        @import "components/_slick-theme";         32:        @import "components/_slack";         33:        //@import "components/_landing";         34:     ->      @ error (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\css\node_modules\css-parse\index.js:57:15)     @ declarations (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\css\node_modules\css-parse\index.js:214:25)     @ rule (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\css\node_modules\css-parse\index.js:481:21)     @ rules (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\css\node_modules\css-parse\index.js:103:56)     @ stylesheet (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\css\node_modules\css-parse\index.js:73:16)     @ object.module.exports [as parse] (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\css\node_modules\css-parse\index.js:485:10)     @ process (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\src\uncss.js:158:22)     @ trycatcher (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\bluebird\js\release\util.js:11:23)     @ promise._settlepromisefromhandler (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\bluebird\js\release\promise.js:488:35)     @ promise._settlepromise (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\bluebird\js\release\promise.js:548:18)     @ promise._settlepromise0 (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\bluebird\js\release\promise.js:593:10)     @ promise._settlepromises (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\bluebird\js\release\promise.js:676:18)     @ promise._fulfill (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\bluebird\js\release\promise.js:617:18)     @ promisearray._resolve (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\bluebird\js\release\promise_array.js:125:19)     @ promisearray._promisefulfilled (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\bluebird\js\release\promise_array.js:143:14)     @ promise._settlepromise (c:\wamp64\www\css-cleanup\node_modules\gulp-uncss\node_modules\uncss\node_modules\bluebird\js\release\promise.js:553:26) 

my gulpfile.js looks this:

var gulp = require('gulp'); var uncss = require('gulp-uncss');  gulp.task('default', function () {     return gulp.src('sass/**/*.scss')         .pipe(uncss({             html: ['index.html']         }))         .pipe(gulp.dest('./css_new/')); });