问在我的服务器上路由css的问题

EN

public
  css
    main.css
    main_b.css
  index.hbs
  index_b.hbs
server
  server.js

const path = require('path');
const fs = require('fs');

const express = require('express');

const app = express();

const hbs = require('hbs');
    
hbs.registerPartials(path.join(__dirname, '../public/partials'));
app.set('view engine', 'hbs');

app.use(express.static(path.join(__dirname, '../public/css')));
    
// activity logger 
app.use((req, res, next) => {
  const now = new Date().toString();
  const logEntry = `${now}: ${req.headers.host} ${req.method}${req.url}`;
  fs.appendFile(path.join(__dirname, '../server/server.log'), logEntry.concat('\n'), (error) => {
    if (error) {
      console.log(error);
    }
  });
  process.env.route = req.path;
  next();
});

app.get('*', (req, res) => {
  switch (process.env.route) {
    case '/': // home page
      res.render('../public/index.hbs');
      break;
    case '/b': // basic layout 
      res.render('../public/index_b.hbs');
      break;
    
    default: // unknown routes
      res.render('../public/index.hbs');
  }
});

app.listen(3000);