How to push html-page into response(SPA)?

Question

HTML

The point is this. I'm trying to write SPA. If I understood correctly, then there should be one HTML file that we will send for each url request. And depending on the url - process, hide\open and fill the elements of the HTML file. So: while using index.html as the start page as a static file ( app.use(express.static(__dirname ))) everything worked fine. But when I decided to send it as a response to the start page

app.get('/', function(req, res, next){
  res.sendfile('index.html')
})

HTML itself loaded, but neither the css file, nor jquery, and even the file with scripts did not want to connect.
Structure:
[\public
\bower_components
\jquery
\dist
jquery.min.js]
app.js
index.html
sripts.js
style.css
I do not rule out (even most likely) that I am stupid and try to do it in an impossible way. Point out the error. Thank you)