We have just performed an upgrade from nopCommerce 1.80 to nopCommerce 1.90 for a site using a custom developed template.
The upgrade itself went smoothly. But...
After the upgrade we found that, again, the css structure has been changed. (It is using camel casing now)

I have two questions:

1) Why the CSS structure is changing, almost, every update?

2) What is the best practice for upgrading custom developed templates?
Rewriting the entire is a lot of work.

Regards,
Dennis