Can you please advise what value/format is supposed to be entered in the Css Class fields?
The CSS Class field should be populated with a CSS Class name. See: Field Prefs/Layout
That class name must be defined in the custom CSS file that you will have setup either for the entire dbFront site or the dbFront database. See:
Suppose you had a specific set of fields that were customer comments that needed to be highlighted. You would:
Add a CSS class named "customerComment",
/* New CSS Class Named "customerComment" */
color: red !important;
background-color: yellow !important;
background-image: none !important;
Set the class name on all appropriate fields to "customerComment".
One you refresh the screen in dbFront then all of the fields with the class "customerComment" would appear as intended.