Anthony you're right. the class .columns is Skeleton. I repeated the case indicated by Massimo without modify other than static/css/ web2py.css (the html code is generated automatically from web2py). The ugly layout depended on the width of the table (containing web2py_grid) inserted in div.columns. So I adjusted the width of the table to that of its container ( div.columns). To avoid misunderstandings I used the selector .columns in css rules.
Paolo
