Problem with CSS linear-gradient

Hi all,
I try to overwrite the background image (linear-gradient) of selected cells in a grid:

.v-grid-row-selected > .v-grid-cell { background-image: linear-gradient(black 33.3%, red 33.3%, red 66.6%, gold 66.6%); } But the compiled CSS I see is

background-image: linear, black 33.3%, red 33.3%, red 66.6%, gold 66.6%; This is not valid and so the background image from original theme is used.
Any ideas? Maybe it’s a bug?
Vaadin 7.6.3
Thanks in advance

Google is your friend… →!/thread/8127922

took me about ten seconds to find it…