I configure browserSync to work through a proxy - why do the styles fly off?

Question

Web development

In the usual configuration of the browserSync task, everything works stably:

gulp.task('browser-sync', function() {
  browserSync({
    server: {
      baseDir: 'app'
    },
    notify: false,
    browser: 'google chrome',
  })
});

When switching to work from a local server, you have to register a proxy:

gulp.task('browser-sync', function() { //In case of php-project
  browserSync({
    proxy: "http://localhost:8888/untitled/app/",
    notify: false,
    browser: 'google chrome',
  })
});

In this case, the styles completely fly off .
What could be the reason?