if the baseCls is not 'x-plain' the background of the flex
element is white, and on some zoom steps it gets taller
than one pixel and appears as a white line
making it have the plain baseCls, so it does not get any
background color and is always invisible
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
bd260569d3