I'm Being bounced around the curriculum! is that normal?

I started from the top, the HTML section, and have been going from one challenge to the next. After putting many hours in I decided to look at the curriculum and noticed that I’ve only finished a portion of the CSS section, before ending up in the front end libraries section! Is it supposed to bounce me around like this! or did i screw something up? please let me know. thank you.

Bugs should always be reported as GitHub Issues. Whenever reporting a bug, please check first that there isn’t already an issue for it and provide as much detail as possible.

so you’re telling me It’s supposed to be linear.