Handlebars is a templating engine, see you can’t use logic-driven code in an HTML file like an if statement or for loop or some data that is not hardcoded, so to make it easier templating engines are used, when you render that file it renders like an HTML file(if you do view source), yes you can use CSS, thing is that syntax of handlebars is a little different from HTML but you can learn it from here

So, I have been recently learning node.js with express.js, and I was shown to use handlebars with it to create more of a dynamic webpage (Traverymedia). So he made a file home.handlebars and no index.html or something like that. So do handlebars replace HTML? Can you write CSS alongside handlebars?