Beginning in 8u40, the CSS engine does not handle correctly relative sub-directories when parsing @import directives. For example, the following declarations work in u20 but not u40:
@import "css/cssImport1.css"
@import "css/cssImport2.css"

The second import is not taken into account, and the parser emit the following message: "CSS error parsing file: .../css/css/cssImport2.css: could not import "css/cssImport2.css".