You can remove the items' float style in order to make the Menu vertical:
.myHorizontalMenu .k-menu .k-item
{
float:none;
}
myHorizontalMenu is a CSS class applied to a parent element of the Menu. Note that since this behavior is still not supported out of the box, the first-level groups will continue to open downwards, not to the right.
Regards,
Dimo
the Telerik team
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