To stay focused on the topic, create a new page for each coding assignment. The coding can relate to your individual project.
Keep it simple. There is a lot less code to get working and you will be able to determine how the elements and properties work. All the coding relates to the current topic, so you aren’t introducing any situations caused by conflicts between old code and new code.
If all your styling is in your .css file, you can link to it for each assignment. Styling will be consistent throughout. This will allow you to refine your site styling as you move through the course. It also demonstrates the importance of CSS.
When it comes to the final project, you can assemble the pieces by copying code from the respective assignments. You know the code works from the assignment, so you will be integrating the pieces. This is a common practice in any development process – unit testing, then integration.