How can I add CSS file in the middle of Gulp.js task?

How can I add CSS file in the middle of a pipe?

gulp.task('css', function () {
  var processors = [
    // list of PostCSS plugins
  ];
  return gulp.src('src/css/style.css') // Add style.css
    .pipe(postcss(processors)) // Use PostCSS
    .pipe(uncss({
        html: ['dist/index.html'] // Remove unused selectors
    }))
  // And here I want to add some other CSS file
    .pipe(nano()) // Minify CSS
    .pipe(gulp.dest('dist/css/'));
});

Gulp-add-src not works with CSS files. .pipe(gulp.src('src/css/other.css')) -> also not works

How can I solve this problem?