Hi Emil, thanks for your reply. I`m a newbie to wordpress. To be honest I would like to stay with 1.7.5. But since the upgrade from 1.7.4. all white widgets fields in sidebars (except on Home!) are shrinking parallel to the browser downsizing. Means, if I scale the window to smaller resolution than 600px the widget fields getting smaller and smaller (ca. 400 px bowser width = ca. 30px widget fields). I did all recommended before - like creating a child theme with your Child Theme example - but I can't figure out the fault.
If you like, here you can take a look: http://niasony.com/en/category/press-en/
But be aware, I`m still trying to fix it! ;)
With 1.7.4 the sidebares scaled perfectly down to ca. 240 px width, but now I`m totally lost. If there is no other chance I will set up a a new, fresh child theme. I love your theme and by the way the few modifications, which cost me a lot of try and error as a bloody beginner. But than I have to do all modifications and standard setups again. Am I right?