Thanks for the hint, the overwriting of an css rule which is used moodle wide was the cause of this behaviour. It is fixed now with the new build .
General help
Can't resize text area
གྲོས་བསྟུན་འདི་བསྡམས་ཡོདཔ་ལས་ ལན་གསལ་བརྐྱབ་མི་ཚུགས་