Less language is an extension of css and less4j compiles it into regular css. Less adds several dynamic features into css: variables, expressions, nested rules, and so on. Less was designed to be compatible with css and any correct css file is also correct less file.
Hi,
Following should import the css contents to the Less output:
Currently when importing CSS files it's not cheched if they should be inlined: https://github.com/SomMeri/less4j/blob/dfd4178b9eb638c2188fcde5f955403d07fca98f/src/main/java/com/github/sommeri/less4j/core/compiler/stages/SingleImportSolver.java#L72
http://lesscss.org/features/#import-options-inline