Background of input-field in 7.31 not changeable

Hi everyone,

since the last update of our portal to 7.31.3301.368423.20141212122425 we have on every input and textarea-field an background-image:

.urTedWhlEnbl {

     url(../common/inputfield/input_bg.gif?...);

}

How can I remove the background-image? In the theme-editor I can change the background-color of input-fields, but not the image.

Someone an idea? We not have access to the filesystem. If we let change the css in the file-system, what happen at the next update?

Best regards,

Sergej Heinrich