human
Solve the following python programming problem given the following code:
def nested(files, config, rel = '') : 
    outroot = os.path.join (outroot ['root'], config ['output'] ['dir']) 
    def outfile_for(infile) : 
        if (rel and infile.startswith (os.path.normpath (rel))) : 
            infile = infile [(len (rel) + 1) :] 
outname = (os.path.splitext (infile) [0] + '.css') 
        return os.path.join (outroot, outname) 
return _compile (files, config, outfile_for) 

    
    

    Fix the buggy line: outroot = os.path.join (outroot ['root'], config ['output'] ['dir'])
assistant
#Here is Python code to fix the buggy line: outroot = os.

outroot = os.path.join (config ['root'], config ['output'] ['dir'])