setting margin more than 200px in css node #time-box will cause black screen

[knm100]

I tried put the time-box on the left-bottom corner of the screen. but when i set the margin more than 200px in css node #time-box, I will got a black screen after running the gtklock in a terminal
my configuration file as follows
config.ini.txt
gtklock.css.txt
gtklockui.xml.txt

Please help to take a look at this issue.

edited:
OS: Arch linux
compositor: labwc-im-git-0.8.1.r50.geaf11fac
gtklock: gtklock-git-4.0.0.r9.g945313d