@GoToLoop Thanks a lot for detailed and sharp insight! I’ve come to the same conclusion making the same investigations. I’ve opened an issue ticket on p5js Editor on Github. What I’ve observed is that the .css file is merged into a element dynamically inserted into the default returned main .html page, as well as JS code. That makes an all inclusive html+css+js .html page sent to the browser. It’s certainly a developpers’ choice. Maybe this way of doing needs .css file considered as an ‘html/text’ file. But I hope it isn’t and it can also work with a ‘text/css’ mime type file so that the problem could be correctly easily with a correct file header. Thanks again!