Hey @clementh29, I totally agree with you codepen can be slow for some projects. Did you pay attention of your file is it Txt or html sometimes you may accidentally save it as text file…
Code pen and local environment is completely different. Code pen did a lot of behind the scene stuff that you normally required to do on a local project.
For instance, using html and body tag.
Hard to tell endless you upload the file
This happens with CSS too. First name you document, then choose file type to .css then add extension .css to your existing file name, and save only then sublime text recognize your .CSS file.
I think that freecodecamp actually promote writing CSS code in style tag because they still have not created a panel to write CSS, in reality it is a bad practice to write CSS in style tags, because the page has to load CSS styles again and again when page loads, hence professional use extra .css file to link it with the html files. This saves time and make page more efficient.
To write and link external css file, just make a .css file in your folder and add the css code as you would have in style tags then link it in html file by adding this code inside head tag like this: