You can add custom css style. This mean that you can customize design of the website for your own neads. Just add style tag inside that custom script cell it will work.
For example let's say that you want to have different header image on mobile (not the same as on desktop)
Or another example might be that you want to have a sticky nav bar that will be attached to the top of the page while you are scrolling:
How to add custom CSS style to your website
- Open your Google Sheet
- Advanced tab