Localhost on Jekyll does not render css: it only renders online

So far I have been building my website on a localhost.

At some point I had to build an extra page. But then I noticed, while designing on my local host, that the css was not being renderd to that new page (except for the index.html).

So I had to add a / to the path <link href="/css/style.css" rel="stylesheet"> So that the css was shown on my new page & build straight from the root.

Ironically this doesnt work on my local host. Which is a bit annoying, because now I can't design my website on my localhost.

Why is Jekyll acting like this? How can I design locally?

Adress of localhost: http://127.0.0.1:4000/boilerplate/

Link to repo: https://github.com/bomengeduld/boilerplate/tree/gh-pages

Your server address should be http://127.0.0.1:4000 without 'boilerplate' (or you should add 'boilerplate' as your baseurl).