jQueryUI datepicker and Webkit css conflict

jQueryUI datepicker and Webkit css conflict

Hello,
when calling the datepicker widget on one page and days are strecheing over the month frame. This happens only with Webkit based browsers, like Safari or iCab. I don't see this behaviour with other browsers.
I'm using a html theme from ThemeFuse and until now they couldn't tell me, where I should look for this.
Any idea where I can look into this?
Thank you
Quwax