Hi Aishak,
The Pro and the Lite versions are completely different plugins, so users can revert back if they chose to.
Because the Pro version has many more features, the CSS class names and the structure may differ. There is a feature to “import from lite” when creating a new search instance, which will import the custom settings from the lite version.
If you had some custom CSS, that will not work, because the class names and the DOM structure is different in the Pro version, because they are separate plugins. It is not the !important, but the class name differences. There are however many more styling options on the back-end, so there is a good chance you can almost do everything you had in custom CSS.
It still might be possible to fix some of the custom CSS you had, by changing all instances of “asl_” to “asp_” in it. If you have the custom CSS, I can take a look if you want to.