Gulp + Stylus (watcher)

gulpfile.js

var gulp = require('gulp');
var stylus = require('gulp-stylus');
var browser_sync = require('browser-sync');
var reload = browser_sync.reload;

gulp.task('stylus', function() {
 return gulp.src('./static/css/*.styl')
  .pipe(stylus())
   .pipe(gulp.dest('./static/css'))
    .pipe(reload({ stream:true }));
});

gulp.task('serve', function() {
 browser_sync({
  server: {
   baseDir: './'
  }
 });
 gulp.watch('./static/css/*.styl', ['stylus']);
});