Why does the staging environment look different than the development environment, even after promoting the Customer Portal page to staging?
The development area may not always look the same as the staging environment area because the code is not being optimized yet.
When you are in the development area because the code is not optimized, you might see a difference between what is showing in the development environment compared to what is showing in the staging environment even after staging your changes.
In most cases that will not be a factor and the view between the development environment and the staging environment should look the same.
One possible reason development mode might not look the same as staging is when there is an issue with the styling that will only manifest itself with the optimization code.
To get a clear and accurate answer of what your view will look like when making changes and testing, it is better to use what you see in the staging environment after staging as an indicator of what you will see in production environment because the staging environment uses optimized code.
Once you are happy with how the staging environment looks you can promote your changes.