Do I have to use IMCE?
No. Acquia Cohesion allows the site builder to select, either use of IMCE or Entity browser for browsing and selecting images.
Acquia Cohesion renames to Site Studio from version 6.2. Tell me more.
You don’t have to add units unless you want to use a specific unit or you’re adding Custom CSS properties.
Modifiers allow you to apply styles to an element when a specific class, id or attribute is present.