I was having a display problem with a Sigma Grid into Yii framework. The gt_grid.css was conflicting with Yii's screen.css with this result:

If I quit screen.css (for example by renaming it) I got the right result:

I finally
solved the issue by adding:
at the end of gt_grid.css file.
(don't forget to empty the "assets" folder or you will not see the changes!)